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 $76.51   9.311%   $83.6338   $83.63   $83.65   $83.60  
  Purchase #2 $168.55   8.775%   $183.3403   $183.34   $183.35   $183.30  
  Purchase #3 $104.83   3.584%   $108.5871   $108.59   $108.60   $108.60  
  Purchase #4 $199.69   13.340%   $226.3286   $226.33   $226.35   $226.30  
  Purchase #5 $126.98   11.448%   $141.5167   $141.52   $141.50   $141.50  
  Purchase #6 $228.63   10.150%   $251.8359   $251.84   $251.85   $251.80  
  Purchase #7 $82.88   6.856%   $88.5623   $88.56   $88.55   $88.60  
  7 purchase totals = $988.07       $1,083.8047   $1,083.81   $1,083.85   $1,083.70