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	$178.60	3.515%	$184.8778	$184.88	$184.90	$184.90
Purchase #2	$206.84	5.808%	$218.8533	$218.85	$218.85	$218.90
Purchase #3	$83.89	11.639%	$93.654	$93.65	$93.65	$93.70
Purchase #4	$118.42	7.289%	$127.0516	$127.05	$127.05	$127.10
Purchase #5	$179.87	12.776%	$202.8502	$202.85	$202.85	$202.90
Purchase #6	$94.76	11.358%	$105.5228	$105.52	$105.50	$105.50
Purchase #7	$12.48	11.573%	$13.9243	$13.92	$13.90	$13.90
7 purchase totals =	$874.86		$946.7340	$946.72	$946.70	$946.90