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 $192.76   11.241%   $214.4282   $214.43   $214.45   $214.40  
  Purchase #2 $96.99   12.204%   $108.8267   $108.83   $108.85   $108.80  
  Purchase #3 $76.62   6.177%   $81.3528   $81.35   $81.35   $81.40  
  Purchase #4 $167.82   7.427%   $180.284   $180.28   $180.30   $180.30  
  Purchase #5 $130.45   3.156%   $134.567   $134.57   $134.55   $134.60  
  Purchase #6 $55.46   6.152%   $58.8719   $58.87   $58.85   $58.90  
  Purchase #7 $40.41   6.437%   $43.0112   $43.01   $43.00   $43.00  
  7 purchase totals = $760.51       $821.3418   $821.34   $821.35   $821.40