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 $126.87   11.379%   $141.3065   $141.31   $141.30   $141.30  
  Purchase #2 $118.95   8.128%   $128.6183   $128.62   $128.60   $128.60  
  Purchase #3 $78.80   12.622%   $88.7461   $88.75   $88.75   $88.70  
  Purchase #4 $184.36   9.124%   $201.181   $201.18   $201.20   $201.20  
  Purchase #5 $243.30   6.690%   $259.5768   $259.58   $259.60   $259.60  
  Purchase #6 $123.42   9.871%   $135.6028   $135.60   $135.60   $135.60  
  Purchase #7 $247.39   13.547%   $280.9039   $280.90   $280.90   $280.90  
  7 purchase totals = $1,123.09       $1,235.9354   $1,235.94   $1,235.95   $1,235.90