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 $144.46   11.804%   $161.5121   $161.51   $161.50   $161.50  
  Purchase #2 $223.43   7.127%   $239.3539   $239.35   $239.35   $239.40  
  Purchase #3 $236.60   7.616%   $254.6195   $254.62   $254.60   $254.60  
  Purchase #4 $233.64   13.631%   $265.4875   $265.49   $265.50   $265.50  
  Purchase #5 $91.58   6.497%   $97.53   $97.53   $97.55   $97.50  
  Purchase #6 $209.28   10.597%   $231.4574   $231.46   $231.45   $231.50  
  Purchase #7 $23.84   6.167%   $25.3102   $25.31   $25.30   $25.30  
  7 purchase totals = $1,162.83       $1,275.2706   $1,275.27   $1,275.25   $1,275.30