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 $53.74   10.323%   $59.2876   $59.29   $59.30   $59.30  
  Purchase #2 $152.53   11.749%   $170.4507   $170.45   $170.45   $170.50  
  Purchase #3 $85.90   10.864%   $95.2322   $95.23   $95.25   $95.20  
  Purchase #4 $229.58   9.422%   $251.211   $251.21   $251.20   $251.20  
  Purchase #5 $139.47   12.575%   $157.0084   $157.01   $157.00   $157.00  
  Purchase #6 $239.68   6.699%   $255.7362   $255.74   $255.75   $255.70  
  Purchase #7 $170.97   13.695%   $194.3843   $194.38   $194.40   $194.40  
  7 purchase totals = $1,071.87       $1,183.3104   $1,183.31   $1,183.35   $1,183.30