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	$105.62	9.408%	$115.5567	$115.56	$115.55	$115.60
Purchase #2	$230.92	9.632%	$253.1622	$253.16	$253.15	$253.20
Purchase #3	$89.63	11.594%	$100.0217	$100.02	$100.00	$100.00
Purchase #4	$164.86	10.119%	$181.5422	$181.54	$181.55	$181.50
Purchase #5	$37.57	8.187%	$40.6459	$40.65	$40.65	$40.60
Purchase #6	$205.32	11.515%	$228.9626	$228.96	$228.95	$229.00
Purchase #7	$54.41	9.667%	$59.6698	$59.67	$59.65	$59.70
7 purchase totals =	$888.33		$979.5611	$979.56	$979.50	$979.60