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 $59.25   6.110%   $62.8702   $62.87   $62.85   $62.90  
  Purchase #2 $133.70   9.268%   $146.0913   $146.09   $146.10   $146.10  
  Purchase #3 $96.75   12.648%   $108.9869   $108.99   $109.00   $109.00  
  Purchase #4 $61.64   8.144%   $66.66   $66.66   $66.65   $66.70  
  Purchase #5 $161.54   5.496%   $170.4182   $170.42   $170.40   $170.40  
  Purchase #6 $233.95   11.711%   $261.3479   $261.35   $261.35   $261.30  
  Purchase #7 $184.77   9.583%   $202.4765   $202.48   $202.50   $202.50  
  7 purchase totals = $931.60       $1,018.8510   $1,018.86   $1,018.85   $1,018.90