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	$81.34	12.300%	$91.3448	$91.34	$91.35	$91.30
Purchase #2	$45.40	11.490%	$50.6165	$50.62	$50.60	$50.60
Purchase #3	$114.27	11.245%	$127.1197	$127.12	$127.10	$127.10
Purchase #4	$144.30	12.643%	$162.5438	$162.54	$162.55	$162.50
Purchase #5	$25.59	4.224%	$26.6709	$26.67	$26.65	$26.70
Purchase #6	$180.48	6.343%	$191.9278	$191.93	$191.95	$191.90
Purchase #7	$110.85	7.564%	$119.2347	$119.23	$119.25	$119.20
7 purchase totals =	$702.23		$769.4582	$769.45	$769.45	$769.30