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	$77.90	3.769%	$80.8361	$80.84	$80.85	$80.80
Purchase #2	$56.32	3.558%	$58.3239	$58.32	$58.30	$58.30
Purchase #3	$29.81	13.375%	$33.7971	$33.80	$33.80	$33.80
Purchase #4	$146.86	12.849%	$165.73	$165.73	$165.75	$165.70
Purchase #5	$234.95	12.559%	$264.4574	$264.46	$264.45	$264.50
Purchase #6	$214.25	11.315%	$238.4924	$238.49	$238.50	$238.50
Purchase #7	$19.30	7.387%	$20.7257	$20.73	$20.75	$20.70
7 purchase totals =	$779.39		$862.3626	$862.37	$862.40	$862.30