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	$39.91	13.772%	$45.4064	$45.41	$45.40	$45.40
Purchase #2	$11.82	10.505%	$13.0617	$13.06	$13.05	$13.10
Purchase #3	$174.50	9.588%	$191.2311	$191.23	$191.25	$191.20
Purchase #4	$49.70	7.656%	$53.505	$53.51	$53.50	$53.50
Purchase #5	$128.38	4.122%	$133.6718	$133.67	$133.65	$133.70
Purchase #6	$72.71	13.792%	$82.7382	$82.74	$82.75	$82.70
Purchase #7	$249.31	12.569%	$280.6458	$280.65	$280.65	$280.60
7 purchase totals =	$726.33		$800.2600	$800.27	$800.25	$800.20