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 $114.43   4.476%   $119.5519   $119.55   $119.55   $119.60  
  Purchase #2 $60.77   9.221%   $66.3736   $66.37   $66.35   $66.40  
  Purchase #3 $21.51   7.121%   $23.0417   $23.04   $23.05   $23.00  
  Purchase #4 $96.48   11.426%   $107.5038   $107.50   $107.50   $107.50  
  Purchase #5 $36.68   5.619%   $38.741   $38.74   $38.75   $38.70  
  Purchase #6 $32.86   13.397%   $37.2623   $37.26   $37.25   $37.30  
  Purchase #7 $67.97   7.620%   $73.1493   $73.15   $73.15   $73.10  
  7 purchase totals = $430.70       $465.6236   $465.61   $465.60   $465.60