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	$88.87	12.196%	$99.7086	$99.71	$99.70	$99.70
Purchase #2	$35.82	9.258%	$39.1362	$39.14	$39.15	$39.10
Purchase #3	$178.60	4.564%	$186.7513	$186.75	$186.75	$186.80
Purchase #4	$74.49	10.480%	$82.2966	$82.30	$82.30	$82.30
Purchase #5	$12.66	3.203%	$13.0655	$13.07	$13.05	$13.10
Purchase #6	$51.34	11.648%	$57.3201	$57.32	$57.30	$57.30
Purchase #7	$229.46	6.272%	$243.8517	$243.85	$243.85	$243.90
7 purchase totals =	$671.24		$722.1300	$722.14	$722.10	$722.20