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 $55.71   11.769%   $62.2665   $62.27   $62.25   $62.30  
  Purchase #2 $170.61   8.264%   $184.7092   $184.71   $184.70   $184.70  
  Purchase #3 $214.58   11.742%   $239.776   $239.78   $239.80   $239.80  
  Purchase #4 $68.36   3.811%   $70.9652   $70.97   $70.95   $71.00  
  Purchase #5 $104.54   10.524%   $115.5418   $115.54   $115.55   $115.50  
  Purchase #6 $206.85   13.573%   $234.9258   $234.93   $234.95   $234.90  
  Purchase #7 $80.44   6.279%   $85.4908   $85.49   $85.50   $85.50  
  7 purchase totals = $901.09       $993.6753   $993.69   $993.70   $993.70