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	$135.42	11.150%	$150.5193	$150.52	$150.50	$150.50
Purchase #2	$32.82	11.175%	$36.4876	$36.49	$36.50	$36.50
Purchase #3	$153.44	10.732%	$169.9072	$169.91	$169.90	$169.90
Purchase #4	$157.50	13.750%	$179.1563	$179.16	$179.15	$179.20
Purchase #5	$212.32	6.261%	$225.6134	$225.61	$225.60	$225.60
Purchase #6	$86.97	7.610%	$93.5884	$93.59	$93.60	$93.60
Purchase #7	$139.79	5.476%	$147.4449	$147.44	$147.45	$147.40
7 purchase totals =	$918.26		$1,002.7171	$1,002.72	$1,002.70	$1,002.70