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 $63.60   3.520%   $65.8387   $65.84   $65.85   $65.80  
  Purchase #2 $76.40   11.638%   $85.2914   $85.29   $85.30   $85.30  
  Purchase #3 $231.56   6.318%   $246.19   $246.19   $246.20   $246.20  
  Purchase #4 $26.68   3.869%   $27.7122   $27.71   $27.70   $27.70  
  Purchase #5 $124.58   8.748%   $135.4783   $135.48   $135.50   $135.50  
  Purchase #6 $245.99   4.240%   $256.42   $256.42   $256.40   $256.40  
  Purchase #7 $193.82   6.251%   $205.9357   $205.94   $205.95   $205.90  
  7 purchase totals = $962.63       $1,022.8663   $1,022.87   $1,022.90   $1,022.80