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 $208.55   7.819%   $224.8565   $224.86   $224.85   $224.90  
  Purchase #2 $135.58   8.662%   $147.3239   $147.32   $147.30   $147.30  
  Purchase #3 $105.62   13.346%   $119.716   $119.72   $119.70   $119.70  
  Purchase #4 $53.99   5.378%   $56.8936   $56.89   $56.90   $56.90  
  Purchase #5 $214.65   6.483%   $228.5658   $228.57   $228.55   $228.60  
  Purchase #6 $247.68   7.415%   $266.0455   $266.05   $266.05   $266.00  
  Purchase #7 $17.55   5.654%   $18.5423   $18.54   $18.55   $18.50  
  7 purchase totals = $983.62       $1,061.9436   $1,061.95   $1,061.90   $1,061.90