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 $119.51   6.430%   $127.1945   $127.19   $127.20   $127.20  
  Purchase #2 $179.68   13.707%   $204.3087   $204.31   $204.30   $204.30  
  Purchase #3 $59.80   10.227%   $65.9157   $65.92   $65.90   $65.90  
  Purchase #4 $239.46   6.396%   $254.7759   $254.78   $254.80   $254.80  
  Purchase #5 $136.76   8.673%   $148.6212   $148.62   $148.60   $148.60  
  Purchase #6 $192.82   4.581%   $201.6531   $201.65   $201.65   $201.70  
  Purchase #7 $115.62   3.129%   $119.2377   $119.24   $119.25   $119.20  
  7 purchase totals = $1,043.65       $1,121.7068   $1,121.71   $1,121.70   $1,121.70