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	$172.52	6.148%	$183.1265	$183.13	$183.15	$183.10
Purchase #2	$30.54	9.307%	$33.3824	$33.38	$33.40	$33.40
Purchase #3	$245.70	8.554%	$266.7172	$266.72	$266.70	$266.70
Purchase #4	$199.88	13.474%	$226.8118	$226.81	$226.80	$226.80
Purchase #5	$170.66	12.247%	$191.5607	$191.56	$191.55	$191.60
Purchase #6	$92.42	12.677%	$104.1361	$104.14	$104.15	$104.10
Purchase #7	$92.88	11.396%	$103.4646	$103.46	$103.45	$103.50
7 purchase totals =	$1,004.60		$1,109.1993	$1,109.20	$1,109.20	$1,109.20