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	$79.37	12.152%	$89.015	$89.02	$89.00	$89.00
Purchase #2	$7.95	8.331%	$8.6123	$8.61	$8.60	$8.60
Purchase #3	$72.73	11.531%	$81.1165	$81.12	$81.10	$81.10
Purchase #4	$72.78	13.364%	$82.5063	$82.51	$82.50	$82.50
Purchase #5	$10.98	7.810%	$11.8375	$11.84	$11.85	$11.80
Purchase #6	$219.63	8.448%	$238.1843	$238.18	$238.20	$238.20
Purchase #7	$39.29	5.855%	$41.5904	$41.59	$41.60	$41.60
7 purchase totals =	$502.73		$552.8623	$552.87	$552.85	$552.80