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	$146.62	13.580%	$166.531	$166.53	$166.55	$166.50
Purchase #2	$209.88	9.562%	$229.9487	$229.95	$229.95	$229.90
Purchase #3	$33.98	5.106%	$35.715	$35.72	$35.70	$35.70
Purchase #4	$28.79	11.585%	$32.1253	$32.13	$32.15	$32.10
Purchase #5	$156.89	11.817%	$175.4297	$175.43	$175.45	$175.40
Purchase #6	$59.45	13.592%	$67.5304	$67.53	$67.55	$67.50
Purchase #7	$194.90	8.241%	$210.9617	$210.96	$210.95	$211.00
7 purchase totals =	$830.51		$918.2418	$918.25	$918.30	$918.10