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 $59.85   8.279%   $64.805   $64.81   $64.80   $64.80  
  Purchase #2 $164.79   7.206%   $176.6648   $176.66   $176.65   $176.70  
  Purchase #3 $31.51   7.173%   $33.7702   $33.77   $33.75   $33.80  
  Purchase #4 $164.26   6.836%   $175.4888   $175.49   $175.50   $175.50  
  Purchase #5 $107.99   10.707%   $119.5525   $119.55   $119.55   $119.60  
  Purchase #6 $157.74   6.616%   $168.1761   $168.18   $168.20   $168.20  
  Purchase #7 $233.63   4.434%   $243.9892   $243.99   $244.00   $244.00  
  7 purchase totals = $919.77       $982.4466   $982.45   $982.45   $982.60