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	$77.41	6.631%	$82.5431	$82.54	$82.55	$82.50
Purchase #2	$84.47	4.631%	$88.3818	$88.38	$88.40	$88.40
Purchase #3	$164.46	6.761%	$175.5791	$175.58	$175.60	$175.60
Purchase #4	$99.27	10.635%	$109.8274	$109.83	$109.85	$109.80
Purchase #5	$143.42	9.544%	$157.108	$157.11	$157.10	$157.10
Purchase #6	$43.66	7.326%	$46.8585	$46.86	$46.85	$46.90
Purchase #7	$41.90	7.252%	$44.9386	$44.94	$44.95	$44.90
7 purchase totals =	$654.59		$705.2365	$705.24	$705.30	$705.20