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 $32.69   9.519%   $35.8018   $35.80   $35.80   $35.80  
  Purchase #2 $113.42   4.103%   $118.0736   $118.07   $118.05   $118.10  
  Purchase #3 $69.97   13.313%   $79.2851   $79.29   $79.30   $79.30  
  Purchase #4 $226.66   6.337%   $241.0234   $241.02   $241.00   $241.00  
  Purchase #5 $197.68   3.196%   $203.9979   $204.00   $204.00   $204.00  
  Purchase #6 $36.42   10.187%   $40.1301   $40.13   $40.15   $40.10  
  Purchase #7 $9.81   8.706%   $10.6641   $10.66   $10.65   $10.70  
  7 purchase totals = $686.65       $728.9760   $728.97   $728.95   $729.00