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 $235.93   3.673%   $244.5957   $244.60   $244.60   $244.60  
  Purchase #2 $224.38   12.743%   $252.9727   $252.97   $252.95   $253.00  
  Purchase #3 $162.26   10.486%   $179.2746   $179.27   $179.25   $179.30  
  Purchase #4 $170.62   9.528%   $186.8767   $186.88   $186.90   $186.90  
  Purchase #5 $62.26   3.159%   $64.2268   $64.23   $64.25   $64.20  
  Purchase #6 $241.59   7.106%   $258.7574   $258.76   $258.75   $258.80  
  Purchase #7 $22.49   6.525%   $23.9575   $23.96   $23.95   $24.00  
  7 purchase totals = $1,119.53       $1,210.6614   $1,210.67   $1,210.65   $1,210.80