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	$52.45	6.222%	$55.7134	$55.71	$55.70	$55.70
Purchase #2	$201.78	11.218%	$224.4157	$224.42	$224.40	$224.40
Purchase #3	$128.34	9.280%	$140.25	$140.25	$140.25	$140.30
Purchase #4	$241.97	13.648%	$274.9941	$274.99	$275.00	$275.00
Purchase #5	$29.91	13.204%	$33.8593	$33.86	$33.85	$33.90
Purchase #6	$216.37	3.480%	$223.8997	$223.90	$223.90	$223.90
Purchase #7	$80.89	12.606%	$91.087	$91.09	$91.10	$91.10
7 purchase totals =	$951.71		$1,044.2192	$1,044.22	$1,044.20	$1,044.30