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 $109.28   9.536%   $119.7009   $119.70   $119.70   $119.70  
  Purchase #2 $87.61   3.392%   $90.5817   $90.58   $90.60   $90.60  
  Purchase #3 $62.98   7.664%   $67.8068   $67.81   $67.80   $67.80  
  Purchase #4 $64.43   8.584%   $69.9607   $69.96   $69.95   $70.00  
  Purchase #5 $237.66   4.199%   $247.6393   $247.64   $247.65   $247.60  
  Purchase #6 $50.51   4.716%   $52.8921   $52.89   $52.90   $52.90  
  Purchase #7 $48.95   8.804%   $53.2596   $53.26   $53.25   $53.30  
  7 purchase totals = $661.42       $701.8411   $701.84   $701.85   $701.90