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 $221.66   8.817%   $241.2038   $241.20   $241.20   $241.20  
  Purchase #2 $62.92   5.862%   $66.6084   $66.61   $66.60   $66.60  
  Purchase #3 $86.30   8.285%   $93.45   $93.45   $93.45   $93.50  
  Purchase #4 $122.98   10.111%   $135.4145   $135.41   $135.40   $135.40  
  Purchase #5 $54.41   13.322%   $61.6585   $61.66   $61.65   $61.70  
  Purchase #6 $200.55   11.652%   $223.9181   $223.92   $223.90   $223.90  
  Purchase #7 $21.29   4.413%   $22.2295   $22.23   $22.25   $22.20  
  7 purchase totals = $770.11       $844.4828   $844.48   $844.45   $844.50