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 $223.37   12.206%   $250.6345   $250.63   $250.65   $250.60  
  Purchase #2 $170.74   11.779%   $190.8515   $190.85   $190.85   $190.90  
  Purchase #3 $100.67   6.257%   $106.9689   $106.97   $106.95   $107.00  
  Purchase #4 $240.64   11.748%   $268.9104   $268.91   $268.90   $268.90  
  Purchase #5 $26.49   4.732%   $27.7435   $27.74   $27.75   $27.70  
  Purchase #6 $191.90   12.297%   $215.4979   $215.50   $215.50   $215.50  
  Purchase #7 $212.30   10.718%   $235.0543   $235.05   $235.05   $235.10  
  7 purchase totals = $1,166.11       $1,295.6610   $1,295.65   $1,295.65   $1,295.70