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	$137.87	12.670%	$155.3381	$155.34	$155.35	$155.30
Purchase #2	$78.43	13.268%	$88.8361	$88.84	$88.85	$88.80
Purchase #3	$87.52	5.446%	$92.2863	$92.29	$92.30	$92.30
Purchase #4	$206.80	4.543%	$216.1949	$216.19	$216.20	$216.20
Purchase #5	$242.98	10.369%	$268.1746	$268.17	$268.15	$268.20
Purchase #6	$182.66	13.839%	$207.9383	$207.94	$207.95	$207.90
Purchase #7	$66.91	7.817%	$72.1404	$72.14	$72.15	$72.10
7 purchase totals =	$1,003.17		$1,100.9087	$1,100.91	$1,100.95	$1,100.80