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 $54.95   5.562%   $58.0063   $58.01   $58.00   $58.00  
  Purchase #2 $137.43   12.196%   $154.191   $154.19   $154.20   $154.20  
  Purchase #3 $122.60   10.837%   $135.8862   $135.89   $135.90   $135.90  
  Purchase #4 $51.97   6.383%   $55.2872   $55.29   $55.30   $55.30  
  Purchase #5 $134.25   6.286%   $142.689   $142.69   $142.70   $142.70  
  Purchase #6 $42.65   9.264%   $46.6011   $46.60   $46.60   $46.60  
  Purchase #7 $105.31   13.590%   $119.6216   $119.62   $119.60   $119.60  
  7 purchase totals = $649.16       $712.2824   $712.29   $712.30   $712.30