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	$53.58	9.188%	$58.5029	$58.50	$58.50	$58.50
Purchase #2	$199.91	10.470%	$220.8406	$220.84	$220.85	$220.80
Purchase #3	$238.88	12.741%	$269.3157	$269.32	$269.30	$269.30
Purchase #4	$40.58	4.215%	$42.2904	$42.29	$42.30	$42.30
Purchase #5	$237.94	11.406%	$265.0794	$265.08	$265.10	$265.10
Purchase #6	$30.93	9.136%	$33.7558	$33.76	$33.75	$33.80
Purchase #7	$146.39	6.739%	$156.2552	$156.26	$156.25	$156.30
7 purchase totals =	$948.21		$1,046.0400	$1,046.05	$1,046.05	$1,046.10