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	$93.71	6.153%	$99.476	$99.48	$99.50	$99.50
Purchase #2	$162.84	7.621%	$175.25	$175.25	$175.25	$175.30
Purchase #3	$71.47	13.160%	$80.8755	$80.88	$80.90	$80.90
Purchase #4	$158.42	12.564%	$178.3239	$178.32	$178.30	$178.30
Purchase #5	$209.68	11.423%	$233.6317	$233.63	$233.65	$233.60
Purchase #6	$116.42	13.304%	$131.9085	$131.91	$131.90	$131.90
Purchase #7	$33.66	9.414%	$36.8288	$36.83	$36.85	$36.80
7 purchase totals =	$846.20		$936.2944	$936.30	$936.35	$936.30