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 $238.73   12.646%   $268.9198   $268.92   $268.90   $268.90  
  Purchase #2 $202.37   11.576%   $225.7964   $225.80   $225.80   $225.80  
  Purchase #3 $80.71   7.581%   $86.8286   $86.83   $86.85   $86.80  
  Purchase #4 $33.49   3.425%   $34.637   $34.64   $34.65   $34.60  
  Purchase #5 $231.64   12.645%   $260.9309   $260.93   $260.95   $260.90  
  Purchase #6 $99.36   4.630%   $103.9604   $103.96   $103.95   $104.00  
  Purchase #7 $144.33   6.157%   $153.2164   $153.22   $153.20   $153.20  
  7 purchase totals = $1,030.63       $1,134.2895   $1,134.30   $1,134.30   $1,134.20