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 $68.62   12.794%   $77.3992   $77.40   $77.40   $77.40  
  Purchase #2 $100.29   13.344%   $113.6727   $113.67   $113.65   $113.70  
  Purchase #3 $36.97   6.537%   $39.3867   $39.39   $39.40   $39.40  
  Purchase #4 $182.46   10.637%   $201.8683   $201.87   $201.85   $201.90  
  Purchase #5 $245.77   11.873%   $274.9503   $274.95   $274.95   $275.00  
  Purchase #6 $177.75   12.289%   $199.5937   $199.59   $199.60   $199.60  
  Purchase #7 $140.39   9.554%   $153.8029   $153.80   $153.80   $153.80  
  7 purchase totals = $952.25       $1,060.6738   $1,060.67   $1,060.65   $1,060.80