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 $235.96   7.549%   $253.7726   $253.77   $253.75   $253.80  
  Purchase #2 $248.62   4.716%   $260.3449   $260.34   $260.35   $260.30  
  Purchase #3 $148.42   11.668%   $165.7376   $165.74   $165.75   $165.70  
  Purchase #4 $48.66   9.341%   $53.2053   $53.21   $53.20   $53.20  
  Purchase #5 $36.68   8.266%   $39.712   $39.71   $39.70   $39.70  
  Purchase #6 $164.84   11.560%   $183.8955   $183.90   $183.90   $183.90  
  Purchase #7 $46.64   4.154%   $48.5774   $48.58   $48.60   $48.60  
  7 purchase totals = $929.82       $1,005.2453   $1,005.25   $1,005.25   $1,005.20