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	$90.90	13.217%	$102.9143	$102.91	$102.90	$102.90
Purchase #2	$159.38	10.295%	$175.7882	$175.79	$175.80	$175.80
Purchase #3	$87.25	3.350%	$90.1729	$90.17	$90.15	$90.20
Purchase #4	$142.38	9.567%	$156.0015	$156.00	$156.00	$156.00
Purchase #5	$164.98	3.470%	$170.7048	$170.70	$170.70	$170.70
Purchase #6	$33.54	12.866%	$37.8553	$37.86	$37.85	$37.90
Purchase #7	$83.86	8.653%	$91.1164	$91.12	$91.10	$91.10
7 purchase totals =	$762.29		$824.5534	$824.55	$824.50	$824.60