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	$84.40	6.435%	$89.8311	$89.83	$89.85	$89.80
Purchase #2	$149.90	12.866%	$169.1861	$169.19	$169.20	$169.20
Purchase #3	$153.39	8.685%	$166.7119	$166.71	$166.70	$166.70
Purchase #4	$63.65	12.749%	$71.7647	$71.76	$71.75	$71.80
Purchase #5	$93.27	4.767%	$97.7162	$97.72	$97.70	$97.70
Purchase #6	$184.45	6.673%	$196.7583	$196.76	$196.75	$196.80
Purchase #7	$109.36	6.597%	$116.5745	$116.57	$116.55	$116.60
7 purchase totals =	$838.42		$908.5428	$908.54	$908.50	$908.60