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 $49.71   6.536%   $52.959   $52.96   $52.95   $53.00  
  Purchase #2 $191.72   8.247%   $207.5311   $207.53   $207.55   $207.50  
  Purchase #3 $55.42   3.502%   $57.3608   $57.36   $57.35   $57.40  
  Purchase #4 $230.77   6.237%   $245.1631   $245.16   $245.15   $245.20  
  Purchase #5 $22.67   3.259%   $23.4088   $23.41   $23.40   $23.40  
  Purchase #6 $124.37   6.600%   $132.5784   $132.58   $132.60   $132.60  
  Purchase #7 $169.91   7.537%   $182.7161   $182.72   $182.70   $182.70  
  7 purchase totals = $844.57       $901.7173   $901.72   $901.70   $901.80