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	$222.28	6.221%	$236.108	$236.11	$236.10	$236.10
Purchase #2	$233.61	13.364%	$264.8296	$264.83	$264.85	$264.80
Purchase #3	$36.91	13.769%	$41.9921	$41.99	$42.00	$42.00
Purchase #4	$63.93	13.329%	$72.4512	$72.45	$72.45	$72.50
Purchase #5	$194.83	10.426%	$215.143	$215.14	$215.15	$215.10
Purchase #6	$208.80	5.827%	$220.9668	$220.97	$220.95	$221.00
Purchase #7	$48.29	12.826%	$54.4837	$54.48	$54.50	$54.50
7 purchase totals =	$1,008.65		$1,105.9744	$1,105.97	$1,106.00	$1,106.00