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 $32.29   7.222%   $34.622   $34.62   $34.60   $34.60  
  Purchase #2 $116.42   7.296%   $124.914   $124.91   $124.90   $124.90  
  Purchase #3 $188.90   6.398%   $200.9858   $200.99   $201.00   $201.00  
  Purchase #4 $133.32   6.202%   $141.5885   $141.59   $141.60   $141.60  
  Purchase #5 $24.71   7.402%   $26.539   $26.54   $26.55   $26.50  
  Purchase #6 $41.96   12.352%   $47.1429   $47.14   $47.15   $47.10  
  Purchase #7 $187.80   12.108%   $210.5388   $210.54   $210.55   $210.50  
  7 purchase totals = $725.40       $786.3310   $786.33   $786.35   $786.20