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 $61.88   3.771%   $64.2135   $64.21   $64.20   $64.20  
  Purchase #2 $112.61   4.580%   $117.7675   $117.77   $117.75   $117.80  
  Purchase #3 $80.75   8.383%   $87.5193   $87.52   $87.50   $87.50  
  Purchase #4 $240.32   3.155%   $247.9021   $247.90   $247.90   $247.90  
  Purchase #5 $113.41   5.209%   $119.3175   $119.32   $119.30   $119.30  
  Purchase #6 $49.91   12.350%   $56.0739   $56.07   $56.05   $56.10  
  Purchase #7 $64.99   5.361%   $68.4741   $68.47   $68.45   $68.50  
  7 purchase totals = $723.87       $761.2679   $761.26   $761.15   $761.30