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 $61.93   5.694%   $65.4563   $65.46   $65.45   $65.50  
  Purchase #2 $188.52   13.528%   $214.023   $214.02   $214.00   $214.00  
  Purchase #3 $244.37   12.742%   $275.5076   $275.51   $275.50   $275.50  
  Purchase #4 $192.74   11.377%   $214.668   $214.67   $214.65   $214.70  
  Purchase #5 $119.68   7.739%   $128.942   $128.94   $128.95   $128.90  
  Purchase #6 $95.42   3.200%   $98.4734   $98.47   $98.45   $98.50  
  Purchase #7 $176.55   5.682%   $186.5816   $186.58   $186.60   $186.60  
  7 purchase totals = $1,079.21       $1,183.6519   $1,183.65   $1,183.60   $1,183.70