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	$248.51	11.222%	$276.3978	$276.40	$276.40	$276.40
Purchase #2	$215.78	10.268%	$237.9363	$237.94	$237.95	$237.90
Purchase #3	$65.46	8.463%	$70.9999	$71.00	$71.00	$71.00
Purchase #4	$190.39	10.182%	$209.7755	$209.78	$209.80	$209.80
Purchase #5	$175.36	7.371%	$188.2858	$188.29	$188.30	$188.30
Purchase #6	$187.86	4.807%	$196.8904	$196.89	$196.90	$196.90
Purchase #7	$35.83	11.830%	$40.0687	$40.07	$40.05	$40.10
7 purchase totals =	$1,119.19		$1,220.3544	$1,220.37	$1,220.40	$1,220.40