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	$86.72	13.436%	$98.3717	$98.37	$98.35	$98.40
Purchase #2	$84.54	5.282%	$89.0054	$89.01	$89.00	$89.00
Purchase #3	$164.82	13.624%	$187.2751	$187.28	$187.30	$187.30
Purchase #4	$177.49	10.215%	$195.6206	$195.62	$195.60	$195.60
Purchase #5	$129.38	11.465%	$144.2134	$144.21	$144.20	$144.20
Purchase #6	$191.48	12.668%	$215.7367	$215.74	$215.75	$215.70
Purchase #7	$92.94	7.121%	$99.5583	$99.56	$99.55	$99.60
7 purchase totals =	$927.37		$1,029.7812	$1,029.79	$1,029.75	$1,029.80