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 $65.83   13.815%   $74.9244   $74.92   $74.90   $74.90  
  Purchase #2 $137.81   11.279%   $153.3536   $153.35   $153.35   $153.40  
  Purchase #3 $160.88   9.518%   $176.1926   $176.19   $176.20   $176.20  
  Purchase #4 $30.41   5.712%   $32.147   $32.15   $32.15   $32.10  
  Purchase #5 $136.97   8.240%   $148.2563   $148.26   $148.25   $148.30  
  Purchase #6 $200.83   12.676%   $226.2872   $226.29   $226.30   $226.30  
  Purchase #7 $156.60   5.468%   $165.1629   $165.16   $165.15   $165.20  
  7 purchase totals = $889.33       $976.3240   $976.32   $976.30   $976.40