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 $87.66   12.203%   $98.3571   $98.36   $98.35   $98.40  
  Purchase #2 $224.39   8.257%   $242.9179   $242.92   $242.90   $242.90  
  Purchase #3 $212.73   6.419%   $226.3851   $226.39   $226.40   $226.40  
  Purchase #4 $112.48   6.449%   $119.7338   $119.73   $119.75   $119.70  
  Purchase #5 $215.44   7.519%   $231.6389   $231.64   $231.65   $231.60  
  Purchase #6 $167.80   11.763%   $187.5383   $187.54   $187.55   $187.50  
  Purchase #7 $83.31   9.197%   $90.972   $90.97   $90.95   $91.00  
  7 purchase totals = $1,103.81       $1,197.5431   $1,197.55   $1,197.55   $1,197.50