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 $24.34   8.206%   $26.3373   $26.34   $26.35   $26.30  
  Purchase #2 $144.90   7.834%   $156.2515   $156.25   $156.25   $156.30  
  Purchase #3 $140.41   7.861%   $151.4476   $151.45   $151.45   $151.40  
  Purchase #4 $85.44   3.647%   $88.556   $88.56   $88.55   $88.60  
  Purchase #5 $199.34   11.121%   $221.5086   $221.51   $221.50   $221.50  
  Purchase #6 $73.46   4.727%   $76.9325   $76.93   $76.95   $76.90  
  Purchase #7 $232.38   9.396%   $254.2144   $254.21   $254.20   $254.20  
  7 purchase totals = $900.27       $975.2479   $975.25   $975.25   $975.20