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	$19.46	11.828%	$21.7617	$21.76	$21.75	$21.80
Purchase #2	$153.36	12.399%	$172.3751	$172.38	$172.40	$172.40
Purchase #3	$98.28	5.113%	$103.3051	$103.31	$103.30	$103.30
Purchase #4	$19.41	9.626%	$21.2784	$21.28	$21.30	$21.30
Purchase #5	$95.37	11.507%	$106.3442	$106.34	$106.35	$106.30
Purchase #6	$179.85	6.179%	$190.9629	$190.96	$190.95	$191.00
Purchase #7	$111.38	12.658%	$125.4785	$125.48	$125.50	$125.50
7 purchase totals =	$677.11		$741.5059	$741.51	$741.55	$741.60