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	$82.63	8.813%	$89.9122	$89.91	$89.90	$89.90
Purchase #2	$26.58	7.354%	$28.5347	$28.53	$28.55	$28.50
Purchase #3	$54.30	9.667%	$59.5492	$59.55	$59.55	$59.50
Purchase #4	$228.51	9.695%	$250.664	$250.66	$250.65	$250.70
Purchase #5	$37.50	11.637%	$41.8639	$41.86	$41.85	$41.90
Purchase #6	$106.52	9.138%	$116.2538	$116.25	$116.25	$116.30
Purchase #7	$79.74	4.391%	$83.2414	$83.24	$83.25	$83.20
7 purchase totals =	$615.78		$670.0192	$670.00	$670.00	$670.00