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 $224.97   9.437%   $246.2004   $246.20   $246.20   $246.20  
  Purchase #2 $68.78   3.569%   $71.2348   $71.23   $71.25   $71.20  
  Purchase #3 $12.45   5.448%   $13.1283   $13.13   $13.15   $13.10  
  Purchase #4 $187.55   10.845%   $207.8898   $207.89   $207.90   $207.90  
  Purchase #5 $247.75   9.831%   $272.1063   $272.11   $272.10   $272.10  
  Purchase #6 $227.67   5.377%   $239.9118   $239.91   $239.90   $239.90  
  Purchase #7 $135.28   12.815%   $152.6161   $152.62   $152.60   $152.60  
  7 purchase totals = $1,104.45       $1,203.0875   $1,203.09   $1,203.10   $1,203.00