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 $233.35   12.411%   $262.3111   $262.31   $262.30   $262.30  
  Purchase #2 $176.78   13.506%   $200.6559   $200.66   $200.65   $200.70  
  Purchase #3 $202.61   6.388%   $215.5527   $215.55   $215.55   $215.60  
  Purchase #4 $137.64   5.709%   $145.4979   $145.50   $145.50   $145.50  
  Purchase #5 $230.98   3.557%   $239.196   $239.20   $239.20   $239.20  
  Purchase #6 $113.51   4.170%   $118.2434   $118.24   $118.25   $118.20  
  Purchase #7 $36.60   4.737%   $38.3337   $38.33   $38.35   $38.30  
  7 purchase totals = $1,131.47       $1,219.7907   $1,219.79   $1,219.80   $1,219.80