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 $63.45   8.187%   $68.6447   $68.64   $68.65   $68.60  
  Purchase #2 $161.97   13.810%   $184.3381   $184.34   $184.35   $184.30  
  Purchase #3 $18.26   8.126%   $19.7438   $19.74   $19.75   $19.70  
  Purchase #4 $198.84   6.811%   $212.383   $212.38   $212.40   $212.40  
  Purchase #5 $91.56   6.475%   $97.4885   $97.49   $97.50   $97.50  
  Purchase #6 $176.25   4.357%   $183.9292   $183.93   $183.95   $183.90  
  Purchase #7 $76.76   4.234%   $80.01   $80.01   $80.00   $80.00  
  7 purchase totals = $787.09       $846.5373   $846.53   $846.60   $846.40