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 $60.65   5.322%   $63.8778   $63.88   $63.90   $63.90  
  Purchase #2 $174.81   13.865%   $199.0474   $199.05   $199.05   $199.00  
  Purchase #3 $27.78   8.449%   $30.1271   $30.13   $30.15   $30.10  
  Purchase #4 $25.93   11.564%   $28.9285   $28.93   $28.95   $28.90  
  Purchase #5 $59.25   4.113%   $61.687   $61.69   $61.70   $61.70  
  Purchase #6 $64.57   9.262%   $70.5505   $70.55   $70.55   $70.60  
  Purchase #7 $208.68   7.487%   $224.3039   $224.30   $224.30   $224.30  
  7 purchase totals = $621.67       $678.5222   $678.53   $678.60   $678.50