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 $186.86   12.170%   $209.6009   $209.60   $209.60   $209.60  
  Purchase #2 $46.71   9.224%   $51.0185   $51.02   $51.00   $51.00  
  Purchase #3 $59.36   13.737%   $67.5143   $67.51   $67.50   $67.50  
  Purchase #4 $57.81   7.601%   $62.2041   $62.20   $62.20   $62.20  
  Purchase #5 $23.89   3.559%   $24.7402   $24.74   $24.75   $24.70  
  Purchase #6 $21.28   4.811%   $22.3038   $22.30   $22.30   $22.30  
  Purchase #7 $8.90   12.504%   $10.0129   $10.01   $10.00   $10.00  
  7 purchase totals = $404.81       $447.3947   $447.38   $447.35   $447.30