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 $238.69   12.818%   $269.2853   $269.29   $269.30   $269.30  
  Purchase #2 $72.41   5.244%   $76.2072   $76.21   $76.20   $76.20  
  Purchase #3 $77.61   10.186%   $85.5154   $85.52   $85.50   $85.50  
  Purchase #4 $188.73   10.826%   $209.1619   $209.16   $209.15   $209.20  
  Purchase #5 $183.29   11.871%   $205.0484   $205.05   $205.05   $205.00  
  Purchase #6 $238.45   6.650%   $254.3069   $254.31   $254.30   $254.30  
  Purchase #7 $209.48   12.750%   $236.1887   $236.19   $236.20   $236.20  
  7 purchase totals = $1,208.66       $1,335.7138   $1,335.73   $1,335.70   $1,335.70