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	$37.74	5.495%	$39.8138	$39.81	$39.80	$39.80
Purchase #2	$175.60	7.378%	$188.5558	$188.56	$188.55	$188.60
Purchase #3	$202.65	7.206%	$217.253	$217.25	$217.25	$217.30
Purchase #4	$248.74	5.609%	$262.6918	$262.69	$262.70	$262.70
Purchase #5	$90.73	11.263%	$100.9489	$100.95	$100.95	$100.90
Purchase #6	$201.81	11.797%	$225.6175	$225.62	$225.60	$225.60
Purchase #7	$45.33	6.740%	$48.3852	$48.39	$48.40	$48.40
7 purchase totals =	$1,002.60		$1,083.2660	$1,083.27	$1,083.25	$1,083.30