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 $59.38   6.488%   $63.2326   $63.23   $63.25   $63.20  
  Purchase #2 $212.76   3.381%   $219.9534   $219.95   $219.95   $220.00  
  Purchase #3 $125.90   9.233%   $137.5243   $137.52   $137.50   $137.50  
  Purchase #4 $204.29   11.279%   $227.3319   $227.33   $227.35   $227.30  
  Purchase #5 $27.53   4.693%   $28.822   $28.82   $28.80   $28.80  
  Purchase #6 $103.71   9.692%   $113.7616   $113.76   $113.75   $113.80  
  Purchase #7 $180.71   6.180%   $191.8779   $191.88   $191.90   $191.90  
  7 purchase totals = $914.28       $982.5037   $982.49   $982.50   $982.50