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 $56.66   6.343%   $60.2539   $60.25   $60.25   $60.30  
  Purchase #2 $97.89   8.618%   $106.3262   $106.33   $106.35   $106.30  
  Purchase #3 $213.26   4.779%   $223.4517   $223.45   $223.45   $223.50  
  Purchase #4 $110.47   4.347%   $115.2721   $115.27   $115.25   $115.30  
  Purchase #5 $180.56   11.654%   $201.6025   $201.60   $201.60   $201.60  
  Purchase #6 $125.59   9.549%   $137.5826   $137.58   $137.60   $137.60  
  Purchase #7 $86.56   6.805%   $92.4504   $92.45   $92.45   $92.50  
  7 purchase totals = $870.99       $936.9394   $936.93   $936.95   $937.10