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	$116.48	6.227%	$123.7332	$123.73	$123.75	$123.70
Purchase #2	$188.44	3.357%	$194.7659	$194.77	$194.75	$194.80
Purchase #3	$166.71	7.855%	$179.8051	$179.81	$179.80	$179.80
Purchase #4	$64.61	10.644%	$71.4871	$71.49	$71.50	$71.50
Purchase #5	$242.91	10.224%	$267.7451	$267.75	$267.75	$267.70
Purchase #6	$112.44	13.430%	$127.5407	$127.54	$127.55	$127.50
Purchase #7	$122.90	9.371%	$134.417	$134.42	$134.40	$134.40
7 purchase totals =	$1,014.49		$1,099.4941	$1,099.51	$1,099.50	$1,099.40