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 $214.25   12.209%   $240.4078   $240.41   $240.40   $240.40  
  Purchase #2 $61.43   10.635%   $67.9631   $67.96   $67.95   $68.00  
  Purchase #3 $227.95   10.592%   $252.0945   $252.09   $252.10   $252.10  
  Purchase #4 $45.67   6.605%   $48.6865   $48.69   $48.70   $48.70  
  Purchase #5 $107.84   8.682%   $117.2027   $117.20   $117.20   $117.20  
  Purchase #6 $230.47   10.212%   $254.0056   $254.01   $254.00   $254.00  
  Purchase #7 $72.89   3.107%   $75.1547   $75.15   $75.15   $75.20  
  7 purchase totals = $960.50       $1,055.5149   $1,055.51   $1,055.50   $1,055.60