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 $153.62   6.826%   $164.1061   $164.11   $164.10   $164.10  
  Purchase #2 $37.72   9.231%   $41.2019   $41.20   $41.20   $41.20  
  Purchase #3 $101.39   11.329%   $112.8765   $112.88   $112.90   $112.90  
  Purchase #4 $185.83   6.366%   $197.6599   $197.66   $197.65   $197.70  
  Purchase #5 $179.62   12.393%   $201.8803   $201.88   $201.90   $201.90  
  Purchase #6 $118.98   12.154%   $133.4408   $133.44   $133.45   $133.40  
  Purchase #7 $175.45   5.513%   $185.1226   $185.12   $185.10   $185.10  
  7 purchase totals = $952.61       $1,036.2881   $1,036.29   $1,036.30   $1,036.30