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 $58.49   10.430%   $64.5905   $64.59   $64.60   $64.60  
  Purchase #2 $174.88   11.862%   $195.6243   $195.62   $195.60   $195.60  
  Purchase #3 $88.70   5.502%   $93.5803   $93.58   $93.60   $93.60  
  Purchase #4 $139.35   12.618%   $156.9332   $156.93   $156.95   $156.90  
  Purchase #5 $175.64   8.157%   $189.967   $189.97   $189.95   $190.00  
  Purchase #6 $107.77   4.478%   $112.5959   $112.60   $112.60   $112.60  
  Purchase #7 $31.60   13.278%   $35.7958   $35.80   $35.80   $35.80  
  7 purchase totals = $776.43       $849.0870   $849.09   $849.10   $849.10