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	$86.60	3.753%	$89.8501	$89.85	$89.85	$89.90
Purchase #2	$67.90	12.516%	$76.3984	$76.40	$76.40	$76.40
Purchase #3	$94.86	11.275%	$105.5555	$105.56	$105.55	$105.60
Purchase #4	$191.66	5.417%	$202.0422	$202.04	$202.05	$202.00
Purchase #5	$210.57	5.764%	$222.7073	$222.71	$222.70	$222.70
Purchase #6	$71.53	4.125%	$74.4806	$74.48	$74.50	$74.50
Purchase #7	$139.49	7.658%	$150.1721	$150.17	$150.15	$150.20
7 purchase totals =	$862.61		$921.2062	$921.21	$921.20	$921.30