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 $225.63   8.697%   $245.253   $245.25   $245.25   $245.30  
  Purchase #2 $11.79   13.412%   $13.3713   $13.37   $13.35   $13.40  
  Purchase #3 $25.55   6.251%   $27.1471   $27.15   $27.15   $27.10  
  Purchase #4 $184.81   10.479%   $204.1762   $204.18   $204.20   $204.20  
  Purchase #5 $193.95   12.617%   $218.4207   $218.42   $218.40   $218.40  
  Purchase #6 $150.31   8.697%   $163.3825   $163.38   $163.40   $163.40  
  Purchase #7 $34.75   7.105%   $37.219   $37.22   $37.20   $37.20  
  7 purchase totals = $826.79       $908.9698   $908.97   $908.95   $909.00