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 $176.99   11.116%   $196.6642   $196.66   $196.65   $196.70  
  Purchase #2 $124.70   5.743%   $131.8615   $131.86   $131.85   $131.90  
  Purchase #3 $97.39   4.776%   $102.0413   $102.04   $102.05   $102.00  
  Purchase #4 $214.77   5.626%   $226.853   $226.85   $226.85   $226.90  
  Purchase #5 $36.81   9.260%   $40.2186   $40.22   $40.20   $40.20  
  Purchase #6 $42.79   9.369%   $46.799   $46.80   $46.80   $46.80  
  Purchase #7 $187.35   12.218%   $210.2404   $210.24   $210.25   $210.20  
  7 purchase totals = $880.80       $954.6780   $954.67   $954.65   $954.70