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 $246.59   10.204%   $271.752   $271.75   $271.75   $271.80  
  Purchase #2 $205.99   5.347%   $217.0043   $217.00   $217.00   $217.00  
  Purchase #3 $166.80   8.572%   $181.0981   $181.10   $181.10   $181.10  
  Purchase #4 $206.41   8.869%   $224.7165   $224.72   $224.70   $224.70  
  Purchase #5 $232.30   9.767%   $254.9887   $254.99   $255.00   $255.00  
  Purchase #6 $30.49   7.866%   $32.8883   $32.89   $32.90   $32.90  
  Purchase #7 $76.69   11.598%   $85.5845   $85.58   $85.60   $85.60  
  7 purchase totals = $1,165.27       $1,268.0324   $1,268.03   $1,268.05   $1,268.10