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	$144.59	3.770%	$150.041	$150.04	$150.05	$150.00
Purchase #2	$250.49	3.547%	$259.3749	$259.37	$259.35	$259.40
Purchase #3	$15.91	6.173%	$16.8921	$16.89	$16.90	$16.90
Purchase #4	$103.58	3.214%	$106.9091	$106.91	$106.90	$106.90
Purchase #5	$188.97	11.602%	$210.8943	$210.89	$210.90	$210.90
Purchase #6	$72.34	9.584%	$79.2731	$79.27	$79.25	$79.30
Purchase #7	$172.45	13.354%	$195.479	$195.48	$195.50	$195.50
7 purchase totals =	$948.33		$1,018.8635	$1,018.85	$1,018.85	$1,018.90