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	$77.96	13.165%	$88.2234	$88.22	$88.20	$88.20
Purchase #2	$41.82	10.803%	$46.3378	$46.34	$46.35	$46.30
Purchase #3	$89.36	12.795%	$100.7936	$100.79	$100.80	$100.80
Purchase #4	$83.60	5.853%	$88.4931	$88.49	$88.50	$88.50
Purchase #5	$137.54	7.828%	$148.3066	$148.31	$148.30	$148.30
Purchase #6	$92.42	12.732%	$104.1869	$104.19	$104.20	$104.20
Purchase #7	$79.76	7.326%	$85.6032	$85.60	$85.60	$85.60
7 purchase totals =	$602.46		$661.9446	$661.94	$661.95	$661.90