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	$84.67	7.175%	$90.7451	$90.75	$90.75	$90.70
Purchase #2	$164.63	12.297%	$184.8746	$184.87	$184.85	$184.90
Purchase #3	$142.81	6.632%	$152.2812	$152.28	$152.30	$152.30
Purchase #4	$135.30	13.113%	$153.0419	$153.04	$153.05	$153.00
Purchase #5	$42.57	10.808%	$47.171	$47.17	$47.15	$47.20
Purchase #6	$80.77	11.352%	$89.939	$89.94	$89.95	$89.90
Purchase #7	$161.66	5.825%	$171.0767	$171.08	$171.10	$171.10
7 purchase totals =	$812.41		$889.1295	$889.13	$889.15	$889.10