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	$106.72	4.421%	$111.4381	$111.44	$111.45	$111.40
Purchase #2	$51.45	13.623%	$58.459	$58.46	$58.45	$58.50
Purchase #3	$226.77	7.441%	$243.644	$243.64	$243.65	$243.60
Purchase #4	$244.31	6.333%	$259.7822	$259.78	$259.80	$259.80
Purchase #5	$236.81	5.492%	$249.8156	$249.82	$249.80	$249.80
Purchase #6	$131.73	4.494%	$137.6499	$137.65	$137.65	$137.60
Purchase #7	$250.55	11.733%	$279.947	$279.95	$279.95	$279.90
7 purchase totals =	$1,248.34		$1,340.7358	$1,340.74	$1,340.75	$1,340.60