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 $139.30   11.399%   $155.1788   $155.18   $155.20   $155.20  
  Purchase #2 $110.83   11.473%   $123.5455   $123.55   $123.55   $123.50  
  Purchase #3 $45.89   8.717%   $49.8902   $49.89   $49.90   $49.90  
  Purchase #4 $212.47   10.393%   $234.552   $234.55   $234.55   $234.60  
  Purchase #5 $56.50   6.184%   $59.994   $59.99   $60.00   $60.00  
  Purchase #6 $93.78   7.730%   $101.0292   $101.03   $101.05   $101.00  
  Purchase #7 $245.90   11.437%   $274.0236   $274.02   $274.00   $274.00  
  7 purchase totals = $904.67       $998.2133   $998.21   $998.25   $998.20