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 $114.92   7.688%   $123.755   $123.76   $123.75   $123.80  
  Purchase #2 $75.40   6.192%   $80.0688   $80.07   $80.05   $80.10  
  Purchase #3 $233.48   11.342%   $259.9613   $259.96   $259.95   $260.00  
  Purchase #4 $95.43   11.427%   $106.3348   $106.33   $106.35   $106.30  
  Purchase #5 $58.67   9.866%   $64.4584   $64.46   $64.45   $64.50  
  Purchase #6 $40.83   7.191%   $43.7661   $43.77   $43.75   $43.80  
  Purchase #7 $210.28   6.720%   $224.4108   $224.41   $224.40   $224.40  
  7 purchase totals = $829.01       $902.7552   $902.76   $902.70   $902.90