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 $48.43   8.505%   $52.549   $52.55   $52.55   $52.50  
  Purchase #2 $33.86   12.781%   $38.1876   $38.19   $38.20   $38.20  
  Purchase #3 $166.69   5.791%   $176.343   $176.34   $176.35   $176.30  
  Purchase #4 $85.92   7.441%   $92.3133   $92.31   $92.30   $92.30  
  Purchase #5 $247.67   10.682%   $274.1261   $274.13   $274.15   $274.10  
  Purchase #6 $208.76   13.801%   $237.571   $237.57   $237.55   $237.60  
  Purchase #7 $247.25   12.824%   $278.9573   $278.96   $278.95   $279.00  
  7 purchase totals = $1,038.58       $1,150.0473   $1,150.05   $1,150.05   $1,150.00