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	$40.48	8.486%	$43.9151	$43.92	$43.90	$43.90
Purchase #2	$173.37	13.272%	$196.3797	$196.38	$196.40	$196.40
Purchase #3	$77.95	7.369%	$83.6941	$83.69	$83.70	$83.70
Purchase #4	$168.73	10.394%	$186.2678	$186.27	$186.25	$186.30
Purchase #5	$17.75	3.168%	$18.3123	$18.31	$18.30	$18.30
Purchase #6	$130.37	12.427%	$146.5711	$146.57	$146.55	$146.60
Purchase #7	$237.51	5.442%	$250.4353	$250.44	$250.45	$250.40
7 purchase totals =	$846.16		$925.5754	$925.58	$925.55	$925.60