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	$49.26	3.320%	$50.8954	$50.90	$50.90	$50.90
Purchase #2	$146.34	3.395%	$151.3082	$151.31	$151.30	$151.30
Purchase #3	$83.69	6.416%	$89.0596	$89.06	$89.05	$89.10
Purchase #4	$229.59	13.167%	$259.8201	$259.82	$259.80	$259.80
Purchase #5	$62.68	7.582%	$67.4324	$67.43	$67.45	$67.40
Purchase #6	$174.77	8.570%	$189.7478	$189.75	$189.75	$189.70
Purchase #7	$109.25	3.488%	$113.0606	$113.06	$113.05	$113.10
7 purchase totals =	$855.58		$921.3241	$921.33	$921.30	$921.30