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 $76.67   8.594%   $83.259   $83.26   $83.25   $83.30  
  Purchase #2 $239.48   12.454%   $269.3048   $269.30   $269.30   $269.30  
  Purchase #3 $120.49   6.173%   $127.9278   $127.93   $127.95   $127.90  
  Purchase #4 $118.48   11.763%   $132.4168   $132.42   $132.40   $132.40  
  Purchase #5 $148.54   13.533%   $168.6419   $168.64   $168.65   $168.60  
  Purchase #6 $236.72   7.692%   $254.9285   $254.93   $254.95   $254.90  
  Purchase #7 $132.77   11.440%   $147.9589   $147.96   $147.95   $148.00  
  7 purchase totals = $1,073.15       $1,184.4377   $1,184.44   $1,184.45   $1,184.40