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 $70.74   3.248%   $73.0376   $73.04   $73.05   $73.00  
  Purchase #2 $221.53   13.365%   $251.1375   $251.14   $251.15   $251.10  
  Purchase #3 $243.51   9.655%   $267.0209   $267.02   $267.00   $267.00  
  Purchase #4 $69.60   7.549%   $74.8541   $74.85   $74.85   $74.90  
  Purchase #5 $189.73   6.197%   $201.4876   $201.49   $201.50   $201.50  
  Purchase #6 $216.70   7.828%   $233.6633   $233.66   $233.65   $233.70  
  Purchase #7 $137.63   6.475%   $146.5415   $146.54   $146.55   $146.50  
  7 purchase totals = $1,149.44       $1,247.7425   $1,247.74   $1,247.75   $1,247.70