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 $62.31   10.608%   $68.9198   $68.92   $68.90   $68.90  
  Purchase #2 $103.38   4.114%   $107.6331   $107.63   $107.65   $107.60  
  Purchase #3 $78.34   4.679%   $82.0055   $82.01   $82.00   $82.00  
  Purchase #4 $33.38   7.231%   $35.7937   $35.79   $35.80   $35.80  
  Purchase #5 $77.93   3.291%   $80.4947   $80.49   $80.50   $80.50  
  Purchase #6 $72.64   6.858%   $77.6217   $77.62   $77.60   $77.60  
  Purchase #7 $205.94   9.155%   $224.7938   $224.79   $224.80   $224.80  
  7 purchase totals = $633.92       $677.2623   $677.25   $677.25   $677.20