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	$44.98	13.507%	$51.0554	$51.06	$51.05	$51.10
Purchase #2	$101.54	7.514%	$109.1697	$109.17	$109.15	$109.20
Purchase #3	$73.58	12.198%	$82.5553	$82.56	$82.55	$82.60
Purchase #4	$226.77	12.210%	$254.4586	$254.46	$254.45	$254.50
Purchase #5	$184.50	11.829%	$206.3245	$206.32	$206.30	$206.30
Purchase #6	$51.39	11.161%	$57.1256	$57.13	$57.15	$57.10
Purchase #7	$228.36	6.776%	$243.8337	$243.83	$243.85	$243.80
7 purchase totals =	$911.12		$1,004.5228	$1,004.53	$1,004.50	$1,004.60