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 $61.96   11.521%   $69.0984   $69.10   $69.10   $69.10  
  Purchase #2 $248.61   6.674%   $265.2022   $265.20   $265.20   $265.20  
  Purchase #3 $81.94   10.474%   $90.5224   $90.52   $90.50   $90.50  
  Purchase #4 $32.86   10.304%   $36.2459   $36.25   $36.25   $36.20  
  Purchase #5 $245.35   8.457%   $266.0992   $266.10   $266.10   $266.10  
  Purchase #6 $237.95   9.646%   $260.9027   $260.90   $260.90   $260.90  
  Purchase #7 $205.45   11.843%   $229.7814   $229.78   $229.80   $229.80  
  7 purchase totals = $1,114.12       $1,217.8522   $1,217.85   $1,217.85   $1,217.80