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 $24.33   9.505%   $26.6426   $26.64   $26.65   $26.60  
  Purchase #2 $12.42   4.513%   $12.9805   $12.98   $13.00   $13.00  
  Purchase #3 $73.60   6.767%   $78.5805   $78.58   $78.60   $78.60  
  Purchase #4 $210.97   7.521%   $226.8371   $226.84   $226.85   $226.80  
  Purchase #5 $49.50   12.860%   $55.8657   $55.87   $55.85   $55.90  
  Purchase #6 $240.68   9.285%   $263.0271   $263.03   $263.05   $263.00  
  Purchase #7 $92.69   3.276%   $95.7265   $95.73   $95.75   $95.70  
  7 purchase totals = $704.19       $759.6600   $759.67   $759.75   $759.60