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 $207.61   11.808%   $232.1246   $232.12   $232.10   $232.10  
  Purchase #2 $47.90   3.818%   $49.7288   $49.73   $49.75   $49.70  
  Purchase #3 $179.34   13.677%   $203.8683   $203.87   $203.85   $203.90  
  Purchase #4 $87.92   6.697%   $93.808   $93.81   $93.80   $93.80  
  Purchase #5 $148.51   8.317%   $160.8616   $160.86   $160.85   $160.90  
  Purchase #6 $163.88   3.434%   $169.5076   $169.51   $169.50   $169.50  
  Purchase #7 $124.51   6.267%   $132.313   $132.31   $132.30   $132.30  
  7 purchase totals = $959.67       $1,042.2119   $1,042.21   $1,042.15   $1,042.20