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 $134.39   5.598%   $141.9132   $141.91   $141.90   $141.90  
  Purchase #2 $65.97   10.298%   $72.7636   $72.76   $72.75   $72.80  
  Purchase #3 $110.47   6.549%   $117.7047   $117.70   $117.70   $117.70  
  Purchase #4 $223.94   6.707%   $238.9597   $238.96   $238.95   $239.00  
  Purchase #5 $154.28   12.703%   $173.8782   $173.88   $173.90   $173.90  
  Purchase #6 $60.46   3.426%   $62.5314   $62.53   $62.55   $62.50  
  Purchase #7 $214.60   9.780%   $235.5879   $235.59   $235.60   $235.60  
  7 purchase totals = $964.11       $1,043.3387   $1,043.33   $1,043.35   $1,043.40