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 $62.40   11.124%   $69.3414   $69.34   $69.35   $69.30  
  Purchase #2 $40.85   13.692%   $46.4432   $46.44   $46.45   $46.40  
  Purchase #3 $29.27   4.824%   $30.682   $30.68   $30.70   $30.70  
  Purchase #4 $228.97   4.231%   $238.6577   $238.66   $238.65   $238.70  
  Purchase #5 $82.96   3.857%   $86.1598   $86.16   $86.15   $86.20  
  Purchase #6 $39.99   4.827%   $41.9203   $41.92   $41.90   $41.90  
  Purchase #7 $183.91   4.461%   $192.1142   $192.11   $192.10   $192.10  
  7 purchase totals = $668.35       $705.3186   $705.31   $705.30   $705.30