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 $241.48   8.229%   $261.3514   $261.35   $261.35   $261.40  
  Purchase #2 $159.67   7.546%   $171.7187   $171.72   $171.70   $171.70  
  Purchase #3 $34.97   4.770%   $36.6381   $36.64   $36.65   $36.60  
  Purchase #4 $118.84   5.440%   $125.3049   $125.30   $125.30   $125.30  
  Purchase #5 $228.76   10.727%   $253.2991   $253.30   $253.30   $253.30  
  Purchase #6 $160.34   11.229%   $178.3446   $178.34   $178.35   $178.30  
  Purchase #7 $131.70   10.320%   $145.2914   $145.29   $145.30   $145.30  
  7 purchase totals = $1,075.76       $1,171.9482   $1,171.94   $1,171.95   $1,171.90