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 $47.56   3.659%   $49.3002   $49.30   $49.30   $49.30  
  Purchase #2 $230.78   12.499%   $259.6252   $259.63   $259.65   $259.60  
  Purchase #3 $93.78   3.793%   $97.3371   $97.34   $97.35   $97.30  
  Purchase #4 $120.99   4.303%   $126.1962   $126.20   $126.20   $126.20  
  Purchase #5 $72.52   9.781%   $79.6132   $79.61   $79.60   $79.60  
  Purchase #6 $202.55   13.849%   $230.6011   $230.60   $230.60   $230.60  
  Purchase #7 $167.56   12.149%   $187.9169   $187.92   $187.90   $187.90  
  7 purchase totals = $935.74       $1,030.5899   $1,030.60   $1,030.60   $1,030.50