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 $239.42   11.723%   $267.4872   $267.49   $267.50   $267.50  
  Purchase #2 $66.95   7.733%   $72.1272   $72.13   $72.15   $72.10  
  Purchase #3 $203.55   12.351%   $228.6905   $228.69   $228.70   $228.70  
  Purchase #4 $134.30   10.629%   $148.5747   $148.57   $148.55   $148.60  
  Purchase #5 $95.85   9.249%   $104.7152   $104.72   $104.70   $104.70  
  Purchase #6 $214.55   8.817%   $233.4669   $233.47   $233.45   $233.50  
  Purchase #7 $60.41   8.679%   $65.653   $65.65   $65.65   $65.70  
  7 purchase totals = $1,015.03       $1,120.7147   $1,120.72   $1,120.70   $1,120.80