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 $112.48   6.261%   $119.5224   $119.52   $119.50   $119.50  
  Purchase #2 $93.28   3.119%   $96.1894   $96.19   $96.20   $96.20  
  Purchase #3 $61.40   8.134%   $66.3943   $66.39   $66.40   $66.40  
  Purchase #4 $84.94   10.608%   $93.9504   $93.95   $93.95   $94.00  
  Purchase #5 $155.28   8.568%   $168.5844   $168.58   $168.60   $168.60  
  Purchase #6 $212.37   5.590%   $224.2415   $224.24   $224.25   $224.20  
  Purchase #7 $155.80   10.708%   $172.4831   $172.48   $172.50   $172.50  
  7 purchase totals = $875.55       $941.3655   $941.35   $941.40   $941.40