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 $57.29   8.857%   $62.3642   $62.36   $62.35   $62.40  
  Purchase #2 $36.91   11.159%   $41.0288   $41.03   $41.05   $41.00  
  Purchase #3 $166.45   4.105%   $173.2828   $173.28   $173.30   $173.30  
  Purchase #4 $79.41   3.274%   $82.0099   $82.01   $82.00   $82.00  
  Purchase #5 $108.29   13.578%   $122.9936   $122.99   $123.00   $123.00  
  Purchase #6 $204.65   13.704%   $232.6952   $232.70   $232.70   $232.70  
  Purchase #7 $63.81   10.365%   $70.4239   $70.42   $70.40   $70.40  
  7 purchase totals = $716.81       $784.7984   $784.79   $784.80   $784.80