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 $204.46   5.136%   $214.9611   $214.96   $214.95   $215.00  
  Purchase #2 $215.96   12.310%   $242.5447   $242.54   $242.55   $242.50  
  Purchase #3 $143.45   11.334%   $159.7086   $159.71   $159.70   $159.70  
  Purchase #4 $182.92   10.874%   $202.8107   $202.81   $202.80   $202.80  
  Purchase #5 $86.65   12.345%   $97.3469   $97.35   $97.35   $97.30  
  Purchase #6 $132.59   11.180%   $147.4136   $147.41   $147.40   $147.40  
  Purchase #7 $142.99   13.246%   $161.9305   $161.93   $161.95   $161.90  
  7 purchase totals = $1,109.02       $1,226.7161   $1,226.71   $1,226.70   $1,226.60