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 $172.42   4.455%   $180.1013   $180.10   $180.10   $180.10  
  Purchase #2 $229.65   10.600%   $253.9929   $253.99   $254.00   $254.00  
  Purchase #3 $66.93   13.690%   $76.0927   $76.09   $76.10   $76.10  
  Purchase #4 $171.53   9.574%   $187.9523   $187.95   $187.95   $188.00  
  Purchase #5 $106.55   8.475%   $115.5801   $115.58   $115.60   $115.60  
  Purchase #6 $217.73   3.592%   $225.5509   $225.55   $225.55   $225.60  
  Purchase #7 $188.89   8.454%   $204.8588   $204.86   $204.85   $204.90  
  7 purchase totals = $1,153.70       $1,244.1290   $1,244.12   $1,244.15   $1,244.30