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 $128.59   11.436%   $143.2956   $143.30   $143.30   $143.30  
  Purchase #2 $187.47   8.612%   $203.6149   $203.61   $203.60   $203.60  
  Purchase #3 $207.75   8.221%   $224.8291   $224.83   $224.85   $224.80  
  Purchase #4 $218.73   10.759%   $242.2632   $242.26   $242.25   $242.30  
  Purchase #5 $41.66   9.525%   $45.6281   $45.63   $45.65   $45.60  
  Purchase #6 $88.54   8.676%   $96.2217   $96.22   $96.20   $96.20  
  Purchase #7 $36.66   9.673%   $40.2061   $40.21   $40.20   $40.20  
  7 purchase totals = $909.40       $996.0587   $996.06   $996.05   $996.00