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 $214.98   11.732%   $240.2015   $240.20   $240.20   $240.20  
  Purchase #2 $142.93   3.719%   $148.2456   $148.25   $148.25   $148.20  
  Purchase #3 $178.80   8.202%   $193.4652   $193.47   $193.45   $193.50  
  Purchase #4 $85.48   11.602%   $95.3974   $95.40   $95.40   $95.40  
  Purchase #5 $41.51   7.491%   $44.6195   $44.62   $44.60   $44.60  
  Purchase #6 $246.78   6.835%   $263.6474   $263.65   $263.65   $263.60  
  Purchase #7 $101.37   5.759%   $107.2079   $107.21   $107.20   $107.20  
  7 purchase totals = $1,011.85       $1,092.7845   $1,092.80   $1,092.75   $1,092.70