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	$16.42	7.344%	$17.6259	$17.63	$17.65	$17.60
Purchase #2	$89.51	11.176%	$99.5136	$99.51	$99.50	$99.50
Purchase #3	$221.31	3.872%	$229.8791	$229.88	$229.90	$229.90
Purchase #4	$82.49	10.840%	$91.4319	$91.43	$91.45	$91.40
Purchase #5	$21.56	3.619%	$22.3403	$22.34	$22.35	$22.30
Purchase #6	$130.68	10.517%	$144.4236	$144.42	$144.40	$144.40
Purchase #7	$162.54	10.539%	$179.6701	$179.67	$179.65	$179.70
7 purchase totals =	$724.51		$784.8845	$784.88	$784.90	$784.80