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 $232.73   9.192%   $254.1225   $254.12   $254.10   $254.10  
  Purchase #2 $86.67   6.270%   $92.1042   $92.10   $92.10   $92.10  
  Purchase #3 $174.85   5.778%   $184.9528   $184.95   $184.95   $185.00  
  Purchase #4 $231.89   5.745%   $245.2121   $245.21   $245.20   $245.20  
  Purchase #5 $157.48   12.795%   $177.6296   $177.63   $177.65   $177.60  
  Purchase #6 $182.46   11.506%   $203.4538   $203.45   $203.45   $203.50  
  Purchase #7 $53.30   11.456%   $59.406   $59.41   $59.40   $59.40  
  7 purchase totals = $1,119.38       $1,216.8810   $1,216.87   $1,216.85   $1,216.90