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 $171.73   7.712%   $184.9738   $184.97   $184.95   $185.00  
  Purchase #2 $126.73   13.132%   $143.3722   $143.37   $143.35   $143.40  
  Purchase #3 $179.86   7.786%   $193.8639   $193.86   $193.85   $193.90  
  Purchase #4 $54.55   7.824%   $58.818   $58.82   $58.80   $58.80  
  Purchase #5 $191.37   6.353%   $203.5277   $203.53   $203.55   $203.50  
  Purchase #6 $93.73   11.249%   $104.2737   $104.27   $104.25   $104.30  
  Purchase #7 $249.85   3.582%   $258.7996   $258.80   $258.80   $258.80  
  7 purchase totals = $1,067.82       $1,147.6289   $1,147.62   $1,147.55   $1,147.70