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 $90.50   8.239%   $97.9563   $97.96   $97.95   $98.00  
  Purchase #2 $118.53   11.489%   $132.1479   $132.15   $132.15   $132.10  
  Purchase #3 $213.65   11.564%   $238.3565   $238.36   $238.35   $238.40  
  Purchase #4 $241.77   11.166%   $268.766   $268.77   $268.75   $268.80  
  Purchase #5 $219.45   11.828%   $245.4065   $245.41   $245.40   $245.40  
  Purchase #6 $136.26   9.552%   $149.2756   $149.28   $149.30   $149.30  
  Purchase #7 $234.60   12.200%   $263.2212   $263.22   $263.20   $263.20  
  7 purchase totals = $1,254.76       $1,395.1300   $1,395.15   $1,395.10   $1,395.20