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	$171.36	8.137%	$185.3036	$185.30	$185.30	$185.30
Purchase #2	$242.96	13.442%	$275.6187	$275.62	$275.60	$275.60
Purchase #3	$56.48	11.447%	$62.9453	$62.95	$62.95	$62.90
Purchase #4	$216.85	3.136%	$223.6504	$223.65	$223.65	$223.70
Purchase #5	$121.91	9.521%	$133.5171	$133.52	$133.50	$133.50
Purchase #6	$167.76	12.850%	$189.3172	$189.32	$189.30	$189.30
Purchase #7	$85.69	5.446%	$90.3567	$90.36	$90.35	$90.40
7 purchase totals =	$1,063.01		$1,160.7090	$1,160.72	$1,160.65	$1,160.70