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 $233.86   8.464%   $253.6539   $253.65   $253.65   $253.70  
  Purchase #2 $116.35   4.468%   $121.5485   $121.55   $121.55   $121.50  
  Purchase #3 $235.74   3.694%   $244.4482   $244.45   $244.45   $244.40  
  Purchase #4 $103.93   7.307%   $111.5242   $111.52   $111.50   $111.50  
  Purchase #5 $107.39   7.447%   $115.3873   $115.39   $115.40   $115.40  
  Purchase #6 $200.97   13.399%   $227.898   $227.90   $227.90   $227.90  
  Purchase #7 $46.50   7.686%   $50.074   $50.07   $50.05   $50.10  
  7 purchase totals = $1,044.74       $1,124.5341   $1,124.53   $1,124.50   $1,124.50