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 $60.37   3.646%   $62.5711   $62.57   $62.55   $62.60  
  Purchase #2 $224.40   10.530%   $248.0293   $248.03   $248.05   $248.00  
  Purchase #3 $166.61   3.164%   $171.8815   $171.88   $171.90   $171.90  
  Purchase #4 $111.91   12.726%   $126.1517   $126.15   $126.15   $126.20  
  Purchase #5 $22.40   13.458%   $25.4146   $25.41   $25.40   $25.40  
  Purchase #6 $36.71   6.362%   $39.0455   $39.05   $39.05   $39.00  
  Purchase #7 $41.96   8.616%   $45.5753   $45.58   $45.60   $45.60  
  7 purchase totals = $664.36       $718.6690   $718.67   $718.70   $718.70