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 $185.95   10.202%   $204.9206   $204.92   $204.90   $204.90  
  Purchase #2 $33.84   8.454%   $36.7008   $36.70   $36.70   $36.70  
  Purchase #3 $121.98   11.640%   $136.1785   $136.18   $136.20   $136.20  
  Purchase #4 $101.84   3.391%   $105.2934   $105.29   $105.30   $105.30  
  Purchase #5 $66.55   13.711%   $75.6747   $75.67   $75.65   $75.70  
  Purchase #6 $232.36   13.173%   $262.9688   $262.97   $262.95   $263.00  
  Purchase #7 $158.89   8.370%   $172.1891   $172.19   $172.20   $172.20  
  7 purchase totals = $901.41       $993.9259   $993.92   $993.90   $994.00