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	$50.40	7.393%	$54.1261	$54.13	$54.15	$54.10
Purchase #2	$30.96	4.821%	$32.4526	$32.45	$32.45	$32.50
Purchase #3	$116.81	9.395%	$127.7843	$127.78	$127.80	$127.80
Purchase #4	$199.85	11.579%	$222.9906	$222.99	$223.00	$223.00
Purchase #5	$93.32	13.639%	$106.0479	$106.05	$106.05	$106.00
Purchase #6	$148.89	10.401%	$164.376	$164.38	$164.40	$164.40
Purchase #7	$31.73	4.740%	$33.234	$33.23	$33.25	$33.20
7 purchase totals =	$671.96		$741.0115	$741.01	$741.10	$741.00