Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $227.59   10.419%   $251.3026   $251.30   $251.30   $251.30  
  Purchase #2 $143.91   4.652%   $150.6047   $150.60   $150.60   $150.60  
  Purchase #3 $101.64   12.127%   $113.9659   $113.97   $113.95   $114.00  
  Purchase #4 $170.99   10.208%   $188.4447   $188.44   $188.45   $188.40  
  Purchase #5 $128.51   12.530%   $144.6123   $144.61   $144.60   $144.60  
  Purchase #6 $194.48   10.126%   $214.173   $214.17   $214.15   $214.20  
  Purchase #7 $119.87   7.229%   $128.5354   $128.54   $128.55   $128.50  
  7 purchase totals = $1,086.99       $1,191.6386   $1,191.63   $1,191.60   $1,191.60