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 $69.51   11.182%   $77.2826   $77.28   $77.30   $77.30  
  Purchase #2 $59.96   9.571%   $65.6988   $65.70   $65.70   $65.70  
  Purchase #3 $30.62   11.397%   $34.1098   $34.11   $34.10   $34.10  
  Purchase #4 $216.53   8.430%   $234.7835   $234.78   $234.80   $234.80  
  Purchase #5 $178.68   7.419%   $191.9363   $191.94   $191.95   $191.90  
  Purchase #6 $237.80   8.478%   $257.9607   $257.96   $257.95   $258.00  
  Purchase #7 $131.51   13.839%   $149.7097   $149.71   $149.70   $149.70  
  7 purchase totals = $924.61       $1,011.4814   $1,011.48   $1,011.50   $1,011.50