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 $39.32   13.247%   $44.5287   $44.53   $44.55   $44.50  
  Purchase #2 $179.76   7.468%   $193.1845   $193.18   $193.20   $193.20  
  Purchase #3 $232.87   6.163%   $247.2218   $247.22   $247.20   $247.20  
  Purchase #4 $75.92   12.263%   $85.2301   $85.23   $85.25   $85.20  
  Purchase #5 $138.42   13.643%   $157.3046   $157.30   $157.30   $157.30  
  Purchase #6 $144.45   4.830%   $151.4269   $151.43   $151.45   $151.40  
  Purchase #7 $103.63   12.519%   $116.6034   $116.60   $116.60   $116.60  
  7 purchase totals = $914.37       $995.5000   $995.49   $995.55   $995.40