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 $228.92   6.527%   $243.8616   $243.86   $243.85   $243.90  
  Purchase #2 $101.94   9.164%   $111.2818   $111.28   $111.30   $111.30  
  Purchase #3 $11.90   7.194%   $12.7561   $12.76   $12.75   $12.80  
  Purchase #4 $120.71   10.103%   $132.9053   $132.91   $132.90   $132.90  
  Purchase #5 $115.82   3.283%   $119.6224   $119.62   $119.60   $119.60  
  Purchase #6 $120.73   11.583%   $134.7142   $134.71   $134.70   $134.70  
  Purchase #7 $165.54   8.255%   $179.2053   $179.21   $179.20   $179.20  
  7 purchase totals = $865.56       $934.3467   $934.35   $934.30   $934.40