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	$172.86	6.183%	$183.5479	$183.55	$183.55	$183.50
Purchase #2	$35.56	4.752%	$37.2498	$37.25	$37.25	$37.20
Purchase #3	$199.73	11.823%	$223.3441	$223.34	$223.35	$223.30
Purchase #4	$140.72	12.808%	$158.7434	$158.74	$158.75	$158.70
Purchase #5	$59.38	8.172%	$64.2325	$64.23	$64.25	$64.20
Purchase #6	$123.43	5.459%	$130.168	$130.17	$130.15	$130.20
Purchase #7	$76.59	8.361%	$82.9937	$82.99	$83.00	$83.00
7 purchase totals =	$808.27		$880.2794	$880.27	$880.30	$880.10