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	$229.65	5.815%	$243.0041	$243.00	$243.00	$243.00
Purchase #2	$15.46	11.373%	$17.2183	$17.22	$17.20	$17.20
Purchase #3	$80.32	11.510%	$89.5648	$89.56	$89.55	$89.60
Purchase #4	$149.40	7.668%	$160.856	$160.86	$160.85	$160.90
Purchase #5	$146.52	13.147%	$165.783	$165.78	$165.80	$165.80
Purchase #6	$213.67	4.799%	$223.924	$223.92	$223.90	$223.90
Purchase #7	$84.77	13.807%	$96.4742	$96.47	$96.45	$96.50
7 purchase totals =	$919.79		$996.8244	$996.81	$996.75	$996.90