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	$142.88	10.221%	$157.4838	$157.48	$157.50	$157.50
Purchase #2	$166.60	9.405%	$182.2687	$182.27	$182.25	$182.30
Purchase #3	$29.66	11.615%	$33.105	$33.11	$33.10	$33.10
Purchase #4	$207.58	8.192%	$224.585	$224.59	$224.60	$224.60
Purchase #5	$18.55	11.672%	$20.7152	$20.72	$20.70	$20.70
Purchase #6	$226.77	6.154%	$240.7254	$240.73	$240.75	$240.70
Purchase #7	$64.47	12.487%	$72.5204	$72.52	$72.50	$72.50
7 purchase totals =	$856.51		$931.4035	$931.42	$931.40	$931.40