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 $69.46   11.619%   $77.5306   $77.53   $77.55   $77.50  
  Purchase #2 $136.81   11.373%   $152.3694   $152.37   $152.35   $152.40  
  Purchase #3 $91.91   11.683%   $102.6478   $102.65   $102.65   $102.60  
  Purchase #4 $23.91   8.394%   $25.917   $25.92   $25.90   $25.90  
  Purchase #5 $182.78   12.730%   $206.0479   $206.05   $206.05   $206.00  
  Purchase #6 $188.78   6.554%   $201.1526   $201.15   $201.15   $201.20  
  Purchase #7 $24.33   11.803%   $27.2017   $27.20   $27.20   $27.20  
  7 purchase totals = $717.98       $792.8670   $792.87   $792.85   $792.80