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	$77.51	4.658%	$81.1204	$81.12	$81.10	$81.10
Purchase #2	$245.28	12.466%	$275.8566	$275.86	$275.85	$275.90
Purchase #3	$40.58	3.846%	$42.1407	$42.14	$42.15	$42.10
Purchase #4	$64.93	13.566%	$73.7384	$73.74	$73.75	$73.70
Purchase #5	$79.80	6.728%	$85.1689	$85.17	$85.15	$85.20
Purchase #6	$233.94	11.490%	$260.8197	$260.82	$260.80	$260.80
Purchase #7	$31.65	4.386%	$33.0382	$33.04	$33.05	$33.00
7 purchase totals =	$773.69		$851.8829	$851.89	$851.85	$851.80