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	$142.78	5.597%	$150.7714	$150.77	$150.75	$150.80
Purchase #2	$81.87	9.822%	$89.9113	$89.91	$89.90	$89.90
Purchase #3	$190.33	7.775%	$205.1282	$205.13	$205.15	$205.10
Purchase #4	$156.75	10.177%	$172.7024	$172.70	$172.70	$172.70
Purchase #5	$49.49	7.424%	$53.1641	$53.16	$53.15	$53.20
Purchase #6	$93.35	13.345%	$105.8076	$105.81	$105.80	$105.80
Purchase #7	$149.44	8.538%	$162.1992	$162.20	$162.20	$162.20
7 purchase totals =	$864.01		$939.6842	$939.68	$939.65	$939.70