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 $216.94   8.252%   $234.8419   $234.84   $234.85   $234.80  
  Purchase #2 $88.39   7.643%   $95.1456   $95.15   $95.15   $95.10  
  Purchase #3 $195.44   6.271%   $207.696   $207.70   $207.70   $207.70  
  Purchase #4 $59.28   10.774%   $65.6668   $65.67   $65.65   $65.70  
  Purchase #5 $24.27   12.462%   $27.2945   $27.29   $27.30   $27.30  
  Purchase #6 $196.71   10.354%   $217.0774   $217.08   $217.10   $217.10  
  Purchase #7 $43.66   7.567%   $46.9638   $46.96   $46.95   $47.00  
  7 purchase totals = $824.69       $894.6860   $894.69   $894.70   $894.70