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 $186.88   8.722%   $203.1797   $203.18   $203.20   $203.20  
  Purchase #2 $208.61   13.326%   $236.4094   $236.41   $236.40   $236.40  
  Purchase #3 $68.41   10.317%   $75.4679   $75.47   $75.45   $75.50  
  Purchase #4 $189.54   13.488%   $215.1052   $215.11   $215.10   $215.10  
  Purchase #5 $205.87   9.538%   $225.5059   $225.51   $225.50   $225.50  
  Purchase #6 $46.35   4.230%   $48.3106   $48.31   $48.30   $48.30  
  Purchase #7 $189.70   12.609%   $213.6193   $213.62   $213.60   $213.60  
  7 purchase totals = $1,095.36       $1,217.5980   $1,217.61   $1,217.55   $1,217.60