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 $86.41   13.262%   $97.8697   $97.87   $97.85   $97.90  
  Purchase #2 $184.73   6.155%   $196.1001   $196.10   $196.10   $196.10  
  Purchase #3 $33.74   11.819%   $37.7277   $37.73   $37.75   $37.70  
  Purchase #4 $96.32   5.366%   $101.4885   $101.49   $101.50   $101.50  
  Purchase #5 $164.63   8.589%   $178.7701   $178.77   $178.75   $178.80  
  Purchase #6 $210.82   7.156%   $225.9063   $225.91   $225.90   $225.90  
  Purchase #7 $150.79   4.580%   $157.6962   $157.70   $157.70   $157.70  
  7 purchase totals = $927.44       $995.5586   $995.57   $995.55   $995.60