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 $205.63   12.672%   $231.6874   $231.69   $231.70   $231.70  
  Purchase #2 $101.26   8.719%   $110.0889   $110.09   $110.10   $110.10  
  Purchase #3 $54.50   6.276%   $57.9204   $57.92   $57.90   $57.90  
  Purchase #4 $155.91   11.810%   $174.323   $174.32   $174.30   $174.30  
  Purchase #5 $149.79   3.752%   $155.4101   $155.41   $155.40   $155.40  
  Purchase #6 $144.29   4.633%   $150.975   $150.98   $151.00   $151.00  
  Purchase #7 $84.83   8.169%   $91.7598   $91.76   $91.75   $91.80  
  7 purchase totals = $896.21       $972.1646   $972.17   $972.15   $972.20