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 $79.42   8.862%   $86.4582   $86.46   $86.45   $86.50  
  Purchase #2 $210.26   12.412%   $236.3575   $236.36   $236.35   $236.40  
  Purchase #3 $240.78   12.153%   $270.042   $270.04   $270.05   $270.00  
  Purchase #4 $94.77   11.611%   $105.7737   $105.77   $105.75   $105.80  
  Purchase #5 $21.38   9.325%   $23.3737   $23.37   $23.35   $23.40  
  Purchase #6 $150.31   6.512%   $160.0982   $160.10   $160.10   $160.10  
  Purchase #7 $125.43   7.435%   $134.7557   $134.76   $134.75   $134.80  
  7 purchase totals = $922.35       $1,016.8590   $1,016.86   $1,016.80   $1,017.00