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 $130.85   8.387%   $141.8244   $141.82   $141.80   $141.80  
  Purchase #2 $103.29   7.344%   $110.8756   $110.88   $110.90   $110.90  
  Purchase #3 $195.59   10.788%   $216.6902   $216.69   $216.70   $216.70  
  Purchase #4 $175.97   6.275%   $187.0121   $187.01   $187.00   $187.00  
  Purchase #5 $98.97   8.677%   $107.5576   $107.56   $107.55   $107.60  
  Purchase #6 $23.34   9.193%   $25.4856   $25.49   $25.50   $25.50  
  Purchase #7 $208.59   12.861%   $235.4168   $235.42   $235.40   $235.40  
  7 purchase totals = $936.60       $1,024.8623   $1,024.87   $1,024.85   $1,024.90