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	$26.71	7.179%	$28.6275	$28.63	$28.65	$28.60
Purchase #2	$212.33	12.431%	$238.7247	$238.72	$238.70	$238.70
Purchase #3	$190.52	3.644%	$197.4625	$197.46	$197.45	$197.50
Purchase #4	$191.55	12.478%	$215.4516	$215.45	$215.45	$215.50
Purchase #5	$223.93	8.591%	$243.1678	$243.17	$243.15	$243.20
Purchase #6	$137.91	12.697%	$155.4204	$155.42	$155.40	$155.40
Purchase #7	$84.50	5.827%	$89.4238	$89.42	$89.40	$89.40
7 purchase totals =	$1,067.45		$1,168.2783	$1,168.27	$1,168.20	$1,168.30