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 $83.84   13.761%   $95.3772   $95.38   $95.40   $95.40  
  Purchase #2 $54.94   13.822%   $62.5338   $62.53   $62.55   $62.50  
  Purchase #3 $241.85   7.586%   $260.1967   $260.20   $260.20   $260.20  
  Purchase #4 $160.74   9.629%   $176.2177   $176.22   $176.20   $176.20  
  Purchase #5 $199.66   13.347%   $226.3086   $226.31   $226.30   $226.30  
  Purchase #6 $62.42   12.218%   $70.0465   $70.05   $70.05   $70.00  
  Purchase #7 $82.40   12.495%   $92.6959   $92.70   $92.70   $92.70  
  7 purchase totals = $885.85       $983.3764   $983.39   $983.40   $983.30