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	$73.46	6.441%	$78.1916	$78.19	$78.20	$78.20
Purchase #2	$127.30	11.145%	$141.4876	$141.49	$141.50	$141.50
Purchase #3	$196.56	11.652%	$219.4632	$219.46	$219.45	$219.50
Purchase #4	$141.35	11.616%	$157.7692	$157.77	$157.75	$157.80
Purchase #5	$128.66	8.384%	$139.4469	$139.45	$139.45	$139.40
Purchase #6	$12.80	11.412%	$14.2607	$14.26	$14.25	$14.30
Purchase #7	$42.51	8.386%	$46.0749	$46.07	$46.05	$46.10
7 purchase totals =	$722.64		$796.6941	$796.69	$796.65	$796.80