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	$134.42	10.862%	$149.0207	$149.02	$149.00	$149.00
Purchase #2	$40.36	9.830%	$44.3274	$44.33	$44.35	$44.30
Purchase #3	$143.91	5.653%	$152.0452	$152.05	$152.05	$152.00
Purchase #4	$94.79	11.230%	$105.4349	$105.43	$105.45	$105.40
Purchase #5	$131.39	6.465%	$139.8844	$139.88	$139.90	$139.90
Purchase #6	$45.27	5.721%	$47.8599	$47.86	$47.85	$47.90
Purchase #7	$157.49	9.144%	$171.8909	$171.89	$171.90	$171.90
7 purchase totals =	$747.63		$810.4634	$810.46	$810.50	$810.40