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	$243.81	9.659%	$267.3596	$267.36	$267.35	$267.40
Purchase #2	$64.93	11.867%	$72.6352	$72.64	$72.65	$72.60
Purchase #3	$222.27	6.353%	$236.3908	$236.39	$236.40	$236.40
Purchase #4	$19.51	6.329%	$20.7448	$20.74	$20.75	$20.70
Purchase #5	$102.75	3.586%	$106.4346	$106.43	$106.45	$106.40
Purchase #6	$193.56	10.873%	$214.6058	$214.61	$214.60	$214.60
Purchase #7	$78.83	8.792%	$85.7607	$85.76	$85.75	$85.80
7 purchase totals =	$925.66		$1,003.9315	$1,003.93	$1,003.95	$1,003.90