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	$228.27	11.799%	$255.2036	$255.20	$255.20	$255.20
Purchase #2	$27.79	3.172%	$28.6715	$28.67	$28.65	$28.70
Purchase #3	$198.75	11.369%	$221.3459	$221.35	$221.35	$221.30
Purchase #4	$174.79	3.818%	$181.4635	$181.46	$181.45	$181.50
Purchase #5	$27.41	12.606%	$30.8653	$30.87	$30.85	$30.90
Purchase #6	$143.61	11.717%	$160.4368	$160.44	$160.45	$160.40
Purchase #7	$240.59	5.337%	$253.4303	$253.43	$253.45	$253.40
7 purchase totals =	$1,041.21		$1,131.4169	$1,131.42	$1,131.40	$1,131.40