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 $24.45   8.201%   $26.4551   $26.46   $26.45   $26.50  
  Purchase #2 $161.43   9.154%   $176.2073   $176.21   $176.20   $176.20  
  Purchase #3 $94.93   7.747%   $102.2842   $102.28   $102.30   $102.30  
  Purchase #4 $95.62   9.322%   $104.5337   $104.53   $104.55   $104.50  
  Purchase #5 $147.65   6.280%   $156.9224   $156.92   $156.90   $156.90  
  Purchase #6 $225.49   3.290%   $232.9086   $232.91   $232.90   $232.90  
  Purchase #7 $30.32   6.760%   $32.3696   $32.37   $32.35   $32.40  
  7 purchase totals = $779.89       $831.6809   $831.68   $831.65   $831.70