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	$101.57	8.694%	$110.4005	$110.40	$110.40	$110.40
Purchase #2	$152.99	8.439%	$165.9008	$165.90	$165.90	$165.90
Purchase #3	$166.26	9.506%	$182.0647	$182.06	$182.05	$182.10
Purchase #4	$84.91	6.783%	$90.6694	$90.67	$90.65	$90.70
Purchase #5	$43.80	4.626%	$45.8262	$45.83	$45.85	$45.80
Purchase #6	$222.56	3.183%	$229.6441	$229.64	$229.65	$229.60
Purchase #7	$29.65	10.627%	$32.8009	$32.80	$32.80	$32.80
7 purchase totals =	$801.74		$857.3066	$857.30	$857.30	$857.30