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	$55.88	9.479%	$61.1769	$61.18	$61.20	$61.20
Purchase #2	$36.58	6.696%	$39.0294	$39.03	$39.05	$39.00
Purchase #3	$221.69	13.538%	$251.7024	$251.70	$251.70	$251.70
Purchase #4	$191.89	10.721%	$212.4625	$212.46	$212.45	$212.50
Purchase #5	$150.39	4.186%	$156.6853	$156.69	$156.70	$156.70
Purchase #6	$45.88	3.443%	$47.4596	$47.46	$47.45	$47.50
Purchase #7	$84.89	4.866%	$89.0207	$89.02	$89.00	$89.00
7 purchase totals =	$787.20		$857.5368	$857.54	$857.55	$857.60