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	$71.25	11.414%	$79.3825	$79.38	$79.40	$79.40
Purchase #2	$53.82	7.810%	$58.0233	$58.02	$58.00	$58.00
Purchase #3	$219.41	12.147%	$246.0617	$246.06	$246.05	$246.10
Purchase #4	$65.82	10.723%	$72.8779	$72.88	$72.90	$72.90
Purchase #5	$61.28	11.524%	$68.3419	$68.34	$68.35	$68.30
Purchase #6	$99.46	4.663%	$104.0978	$104.10	$104.10	$104.10
Purchase #7	$144.39	7.708%	$155.5196	$155.52	$155.50	$155.50
7 purchase totals =	$715.43		$784.3047	$784.30	$784.30	$784.30