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 $240.74   8.649%   $261.5616   $261.56   $261.55   $261.60  
  Purchase #2 $117.74   8.407%   $127.6384   $127.64   $127.65   $127.60  
  Purchase #3 $116.92   6.553%   $124.5818   $124.58   $124.60   $124.60  
  Purchase #4 $5.75   3.607%   $5.9574   $5.96   $5.95   $6.00  
  Purchase #5 $51.43   4.508%   $53.7485   $53.75   $53.75   $53.70  
  Purchase #6 $54.56   11.602%   $60.8901   $60.89   $60.90   $60.90  
  Purchase #7 $125.53   6.155%   $133.2564   $133.26   $133.25   $133.30  
  7 purchase totals = $712.67       $767.6342   $767.64   $767.65   $767.70