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 $208.51   10.609%   $230.6308   $230.63   $230.65   $230.60  
  Purchase #2 $128.28   13.695%   $145.8479   $145.85   $145.85   $145.80  
  Purchase #3 $243.44   13.201%   $275.5765   $275.58   $275.60   $275.60  
  Purchase #4 $234.53   3.724%   $243.2639   $243.26   $243.25   $243.30  
  Purchase #5 $14.40   13.438%   $16.3351   $16.34   $16.35   $16.30  
  Purchase #6 $173.53   12.408%   $195.0616   $195.06   $195.05   $195.10  
  Purchase #7 $16.56   8.619%   $17.9873   $17.99   $18.00   $18.00  
  7 purchase totals = $1,019.25       $1,124.7031   $1,124.71   $1,124.75   $1,124.70