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	$146.90	12.737%	$165.6107	$165.61	$165.60	$165.60
Purchase #2	$240.67	6.198%	$255.5867	$255.59	$255.60	$255.60
Purchase #3	$63.30	9.518%	$69.3249	$69.32	$69.30	$69.30
Purchase #4	$136.90	3.472%	$141.6532	$141.65	$141.65	$141.70
Purchase #5	$41.33	10.223%	$45.5552	$45.56	$45.55	$45.60
Purchase #6	$69.80	13.479%	$79.2083	$79.21	$79.20	$79.20
Purchase #7	$28.41	3.286%	$29.3436	$29.34	$29.35	$29.30
7 purchase totals =	$727.31		$786.2826	$786.28	$786.25	$786.30