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 $139.68   8.485%   $151.5318   $151.53   $151.55   $151.50  
  Purchase #2 $26.70   7.381%   $28.6707   $28.67   $28.65   $28.70  
  Purchase #3 $200.61   6.245%   $213.1381   $213.14   $213.15   $213.10  
  Purchase #4 $227.86   5.323%   $239.989   $239.99   $240.00   $240.00  
  Purchase #5 $228.35   11.462%   $254.5235   $254.52   $254.50   $254.50  
  Purchase #6 $107.31   12.306%   $120.5156   $120.52   $120.50   $120.50  
  Purchase #7 $13.56   5.496%   $14.3053   $14.31   $14.30   $14.30  
  7 purchase totals = $944.07       $1,022.6740   $1,022.68   $1,022.65   $1,022.60