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	$94.46	5.272%	$99.4399	$99.44	$99.45	$99.40
Purchase #2	$217.87	7.279%	$233.7288	$233.73	$233.75	$233.70
Purchase #3	$35.27	7.664%	$37.9731	$37.97	$37.95	$38.00
Purchase #4	$104.43	12.554%	$117.5401	$117.54	$117.55	$117.50
Purchase #5	$92.52	11.695%	$103.3402	$103.34	$103.35	$103.30
Purchase #6	$117.98	12.281%	$132.4691	$132.47	$132.45	$132.50
Purchase #7	$97.80	8.217%	$105.8362	$105.84	$105.85	$105.80
7 purchase totals =	$760.33		$830.3274	$830.33	$830.35	$830.20