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	$171.85	4.114%	$178.9199	$178.92	$178.90	$178.90
Purchase #2	$174.58	11.144%	$194.0352	$194.04	$194.05	$194.00
Purchase #3	$81.96	8.800%	$89.1725	$89.17	$89.15	$89.20
Purchase #4	$160.67	7.625%	$172.9211	$172.92	$172.90	$172.90
Purchase #5	$141.41	7.400%	$151.8743	$151.87	$151.85	$151.90
Purchase #6	$189.97	4.841%	$199.1664	$199.17	$199.15	$199.20
Purchase #7	$125.85	3.440%	$130.1792	$130.18	$130.20	$130.20
7 purchase totals =	$1,046.29		$1,116.2686	$1,116.27	$1,116.20	$1,116.30