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 $76.78   9.160%   $83.813   $83.81   $83.80   $83.80  
  Purchase #2 $118.41   5.581%   $125.0185   $125.02   $125.00   $125.00  
  Purchase #3 $158.32   11.775%   $176.9622   $176.96   $176.95   $177.00  
  Purchase #4 $250.55   3.294%   $258.8031   $258.80   $258.80   $258.80  
  Purchase #5 $229.45   5.108%   $241.1703   $241.17   $241.15   $241.20  
  Purchase #6 $102.49   3.446%   $106.0218   $106.02   $106.00   $106.00  
  Purchase #7 $148.54   6.402%   $158.0495   $158.05   $158.05   $158.00  
  7 purchase totals = $1,084.54       $1,149.8384   $1,149.83   $1,149.75   $1,149.80