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 $250.95   12.384%   $282.0276   $282.03   $282.05   $282.00  
  Purchase #2 $44.99   11.561%   $50.1913   $50.19   $50.20   $50.20  
  Purchase #3 $32.95   7.683%   $35.4815   $35.48   $35.50   $35.50  
  Purchase #4 $172.98   12.594%   $194.7651   $194.77   $194.75   $194.80  
  Purchase #5 $191.80   11.757%   $214.3499   $214.35   $214.35   $214.30  
  Purchase #6 $201.58   10.624%   $222.9959   $223.00   $223.00   $223.00  
  Purchase #7 $94.63   3.618%   $98.0537   $98.05   $98.05   $98.10  
  7 purchase totals = $989.88       $1,097.8650   $1,097.87   $1,097.90   $1,097.90