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 $85.89   11.472%   $95.7433   $95.74   $95.75   $95.70  
  Purchase #2 $63.76   8.371%   $69.0973   $69.10   $69.10   $69.10  
  Purchase #3 $202.32   12.794%   $228.2048   $228.20   $228.20   $228.20  
  Purchase #4 $58.48   13.384%   $66.307   $66.31   $66.30   $66.30  
  Purchase #5 $77.83   9.341%   $85.1001   $85.10   $85.10   $85.10  
  Purchase #6 $226.31   13.518%   $256.9026   $256.90   $256.90   $256.90  
  Purchase #7 $47.31   11.750%   $52.8689   $52.87   $52.85   $52.90  
  7 purchase totals = $761.90       $854.2240   $854.22   $854.20   $854.20