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 $202.68   11.532%   $226.0531   $226.05   $226.05   $226.10  
  Purchase #2 $101.67   10.520%   $112.3657   $112.37   $112.35   $112.40  
  Purchase #3 $82.30   6.693%   $87.8083   $87.81   $87.80   $87.80  
  Purchase #4 $161.81   4.228%   $168.6513   $168.65   $168.65   $168.70  
  Purchase #5 $244.77   10.165%   $269.6509   $269.65   $269.65   $269.70  
  Purchase #6 $124.68   5.788%   $131.8965   $131.90   $131.90   $131.90  
  Purchase #7 $33.32   13.432%   $37.7955   $37.80   $37.80   $37.80  
  7 purchase totals = $951.23       $1,034.2213   $1,034.23   $1,034.20   $1,034.40