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	$46.47	5.772%	$49.1522	$49.15	$49.15	$49.20
Purchase #2	$52.33	4.396%	$54.6304	$54.63	$54.65	$54.60
Purchase #3	$29.74	13.797%	$33.8432	$33.84	$33.85	$33.80
Purchase #4	$106.36	9.864%	$116.8514	$116.85	$116.85	$116.90
Purchase #5	$89.64	9.693%	$98.3288	$98.33	$98.35	$98.30
Purchase #6	$237.75	5.288%	$250.3222	$250.32	$250.30	$250.30
Purchase #7	$53.51	11.442%	$59.6326	$59.63	$59.65	$59.60
7 purchase totals =	$615.80		$662.7608	$662.75	$662.80	$662.70