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	$93.30	6.468%	$99.3346	$99.33	$99.35	$99.30
Purchase #2	$174.85	7.784%	$188.4603	$188.46	$188.45	$188.50
Purchase #3	$137.36	13.426%	$155.802	$155.80	$155.80	$155.80
Purchase #4	$25.88	9.228%	$28.2682	$28.27	$28.25	$28.30
Purchase #5	$74.75	4.237%	$77.9172	$77.92	$77.90	$77.90
Purchase #6	$26.28	12.414%	$29.5424	$29.54	$29.55	$29.50
Purchase #7	$53.83	6.865%	$57.5254	$57.53	$57.55	$57.50
7 purchase totals =	$586.25		$636.8501	$636.85	$636.85	$636.80