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 $23.39   8.586%   $25.3983   $25.40   $25.40   $25.40  
  Purchase #2 $191.41   4.137%   $199.3286   $199.33   $199.35   $199.30  
  Purchase #3 $34.84   10.477%   $38.4902   $38.49   $38.50   $38.50  
  Purchase #4 $23.90   11.817%   $26.7243   $26.72   $26.70   $26.70  
  Purchase #5 $175.58   5.313%   $184.9086   $184.91   $184.90   $184.90  
  Purchase #6 $156.41   6.288%   $166.2451   $166.25   $166.25   $166.20  
  Purchase #7 $69.65   12.822%   $78.5805   $78.58   $78.60   $78.60  
  7 purchase totals = $675.18       $719.6756   $719.68   $719.70   $719.60