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 $184.52   12.217%   $207.0628   $207.06   $207.05   $207.10  
  Purchase #2 $70.90   3.176%   $73.1518   $73.15   $73.15   $73.20  
  Purchase #3 $187.92   7.506%   $202.0253   $202.03   $202.05   $202.00  
  Purchase #4 $151.74   8.249%   $164.257   $164.26   $164.25   $164.30  
  Purchase #5 $6.93   9.846%   $7.6123   $7.61   $7.60   $7.60  
  Purchase #6 $152.89   5.622%   $161.4855   $161.49   $161.50   $161.50  
  Purchase #7 $66.65   4.201%   $69.45   $69.45   $69.45   $69.50  
  7 purchase totals = $821.55       $885.0447   $885.05   $885.05   $885.20