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	$78.94	12.823%	$89.0625	$89.06	$89.05	$89.10
Purchase #2	$82.41	8.403%	$89.3349	$89.33	$89.35	$89.30
Purchase #3	$39.92	10.505%	$44.1136	$44.11	$44.10	$44.10
Purchase #4	$213.59	13.529%	$242.4866	$242.49	$242.50	$242.50
Purchase #5	$5.73	8.834%	$6.2362	$6.24	$6.25	$6.20
Purchase #6	$123.69	10.326%	$136.4622	$136.46	$136.45	$136.50
Purchase #7	$20.90	13.251%	$23.6695	$23.67	$23.65	$23.70
7 purchase totals =	$565.18		$631.3655	$631.36	$631.35	$631.40