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	$53.26	12.427%	$59.8786	$59.88	$59.90	$59.90
Purchase #2	$132.42	7.594%	$142.476	$142.48	$142.50	$142.50
Purchase #3	$91.85	5.828%	$97.203	$97.20	$97.20	$97.20
Purchase #4	$43.39	6.644%	$46.2728	$46.27	$46.25	$46.30
Purchase #5	$55.84	5.622%	$58.9793	$58.98	$59.00	$59.00
Purchase #6	$201.49	13.262%	$228.2116	$228.21	$228.20	$228.20
Purchase #7	$89.89	12.707%	$101.3123	$101.31	$101.30	$101.30
7 purchase totals =	$668.14		$734.3336	$734.33	$734.35	$734.40