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 $248.88   13.386%   $282.1951   $282.20   $282.20   $282.20  
  Purchase #2 $21.42   12.110%   $24.014   $24.01   $24.00   $24.00  
  Purchase #3 $67.81   11.484%   $75.5973   $75.60   $75.60   $75.60  
  Purchase #4 $187.73   5.452%   $197.965   $197.97   $197.95   $198.00  
  Purchase #5 $203.78   9.669%   $223.4835   $223.48   $223.50   $223.50  
  Purchase #6 $77.99   8.219%   $84.4   $84.40   $84.40   $84.40  
  Purchase #7 $5.26   10.681%   $5.8218   $5.82   $5.80   $5.80  
  7 purchase totals = $812.87       $893.4767   $893.48   $893.45   $893.50