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 $59.68   5.409%   $62.9081   $62.91   $62.90   $62.90  
  Purchase #2 $48.95   5.496%   $51.6403   $51.64   $51.65   $51.60  
  Purchase #3 $31.80   7.436%   $34.1646   $34.16   $34.15   $34.20  
  Purchase #4 $86.57   9.812%   $95.0642   $95.06   $95.05   $95.10  
  Purchase #5 $164.98   5.134%   $173.4501   $173.45   $173.45   $173.50  
  Purchase #6 $153.34   11.747%   $171.3528   $171.35   $171.35   $171.40  
  Purchase #7 $24.31   9.784%   $26.6885   $26.69   $26.70   $26.70  
  7 purchase totals = $569.63       $615.2686   $615.26   $615.25   $615.40