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 $63.74   8.349%   $69.0617   $69.06   $69.05   $69.10  
  Purchase #2 $235.44   10.544%   $260.2648   $260.26   $260.25   $260.30  
  Purchase #3 $37.76   3.667%   $39.1447   $39.14   $39.15   $39.10  
  Purchase #4 $208.44   4.255%   $217.3091   $217.31   $217.30   $217.30  
  Purchase #5 $40.25   8.427%   $43.6419   $43.64   $43.65   $43.60  
  Purchase #6 $39.61   6.788%   $42.2987   $42.30   $42.30   $42.30  
  Purchase #7 $148.72   3.813%   $154.3907   $154.39   $154.40   $154.40  
  7 purchase totals = $773.96       $826.1116   $826.10   $826.10   $826.10