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 $14.53   10.374%   $16.0373   $16.04   $16.05   $16.00  
  Purchase #2 $209.72   8.336%   $227.2023   $227.20   $227.20   $227.20  
  Purchase #3 $68.58   6.352%   $72.9362   $72.94   $72.95   $72.90  
  Purchase #4 $210.37   4.178%   $219.1593   $219.16   $219.15   $219.20  
  Purchase #5 $24.99   5.790%   $26.4369   $26.44   $26.45   $26.40  
  Purchase #6 $66.31   3.416%   $68.5751   $68.58   $68.60   $68.60  
  Purchase #7 $86.72   5.513%   $91.5009   $91.50   $91.50   $91.50  
  7 purchase totals = $681.22       $721.8480   $721.86   $721.90   $721.80