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 $18.54   4.457%   $19.3663   $19.37   $19.35   $19.40  
  Purchase #2 $238.33   13.138%   $269.6418   $269.64   $269.65   $269.60  
  Purchase #3 $73.63   3.864%   $76.4751   $76.48   $76.50   $76.50  
  Purchase #4 $166.89   8.194%   $180.565   $180.57   $180.55   $180.60  
  Purchase #5 $42.66   3.152%   $44.0046   $44.00   $44.00   $44.00  
  Purchase #6 $181.60   10.804%   $201.2201   $201.22   $201.20   $201.20  
  Purchase #7 $141.89   13.308%   $160.7727   $160.77   $160.75   $160.80  
  7 purchase totals = $863.54       $952.0456   $952.05   $952.00   $952.10