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	$45.89	6.616%	$48.9261	$48.93	$48.95	$48.90
Purchase #2	$49.79	7.583%	$53.5656	$53.57	$53.55	$53.60
Purchase #3	$158.58	3.564%	$164.2318	$164.23	$164.25	$164.20
Purchase #4	$20.42	9.414%	$22.3423	$22.34	$22.35	$22.30
Purchase #5	$14.27	8.672%	$15.5075	$15.51	$15.50	$15.50
Purchase #6	$150.53	6.648%	$160.5372	$160.54	$160.55	$160.50
Purchase #7	$64.39	10.859%	$71.3821	$71.38	$71.40	$71.40
7 purchase totals =	$503.87		$536.4926	$536.50	$536.55	$536.40