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 $186.77   13.449%   $211.8887   $211.89   $211.90   $211.90  
  Purchase #2 $93.91   3.300%   $97.009   $97.01   $97.00   $97.00  
  Purchase #3 $153.53   3.503%   $158.9082   $158.91   $158.90   $158.90  
  Purchase #4 $54.33   9.249%   $59.355   $59.36   $59.35   $59.40  
  Purchase #5 $250.68   7.724%   $270.0425   $270.04   $270.05   $270.00  
  Purchase #6 $71.36   4.469%   $74.5491   $74.55   $74.55   $74.50  
  Purchase #7 $159.86   7.775%   $172.2891   $172.29   $172.30   $172.30  
  7 purchase totals = $970.44       $1,044.0416   $1,044.05   $1,044.05   $1,044.00