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 $224.64   9.334%   $245.6079   $245.61   $245.60   $245.60  
  Purchase #2 $168.89   9.381%   $184.7336   $184.73   $184.75   $184.70  
  Purchase #3 $145.61   8.579%   $158.1019   $158.10   $158.10   $158.10  
  Purchase #4 $207.94   13.462%   $235.9329   $235.93   $235.95   $235.90  
  Purchase #5 $231.73   6.107%   $245.8818   $245.88   $245.90   $245.90  
  Purchase #6 $111.91   8.369%   $121.2757   $121.28   $121.30   $121.30  
  Purchase #7 $133.86   9.177%   $146.1443   $146.14   $146.15   $146.10  
  7 purchase totals = $1,224.58       $1,337.6781   $1,337.67   $1,337.75   $1,337.60