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 $67.62   13.341%   $76.6412   $76.64   $76.65   $76.60  
  Purchase #2 $246.68   11.481%   $275.0013   $275.00   $275.00   $275.00  
  Purchase #3 $121.74   8.808%   $132.4629   $132.46   $132.45   $132.50  
  Purchase #4 $110.52   13.838%   $125.8138   $125.81   $125.80   $125.80  
  Purchase #5 $247.51   8.804%   $269.3008   $269.30   $269.30   $269.30  
  Purchase #6 $182.88   4.580%   $191.2559   $191.26   $191.25   $191.30  
  Purchase #7 $185.81   12.838%   $209.6643   $209.66   $209.65   $209.70  
  7 purchase totals = $1,162.76       $1,280.1402   $1,280.13   $1,280.10   $1,280.20