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	$187.90	8.643%	$204.1402	$204.14	$204.15	$204.10
Purchase #2	$35.74	12.821%	$40.3222	$40.32	$40.30	$40.30
Purchase #3	$81.98	8.777%	$89.1754	$89.18	$89.20	$89.20
Purchase #4	$142.31	5.581%	$150.2523	$150.25	$150.25	$150.30
Purchase #5	$64.45	4.366%	$67.2639	$67.26	$67.25	$67.30
Purchase #6	$165.82	10.653%	$183.4848	$183.48	$183.50	$183.50
Purchase #7	$219.31	10.160%	$241.5919	$241.59	$241.60	$241.60
7 purchase totals =	$897.51		$976.2307	$976.22	$976.25	$976.30