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	$83.93	6.834%	$89.6658	$89.67	$89.65	$89.70
Purchase #2	$111.55	11.333%	$124.192	$124.19	$124.20	$124.20
Purchase #3	$199.92	8.210%	$216.3334	$216.33	$216.35	$216.30
Purchase #4	$147.40	10.504%	$162.8829	$162.88	$162.90	$162.90
Purchase #5	$181.37	6.708%	$193.5363	$193.54	$193.55	$193.50
Purchase #6	$52.73	3.349%	$54.4959	$54.50	$54.50	$54.50
Purchase #7	$224.62	13.579%	$255.1211	$255.12	$255.10	$255.10
7 purchase totals =	$1,001.52		$1,096.2274	$1,096.23	$1,096.25	$1,096.20