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	$6.44	4.365%	$6.7211	$6.72	$6.70	$6.70
Purchase #2	$162.54	13.392%	$184.3074	$184.31	$184.30	$184.30
Purchase #3	$142.59	12.269%	$160.0844	$160.08	$160.10	$160.10
Purchase #4	$232.56	5.159%	$244.5578	$244.56	$244.55	$244.60
Purchase #5	$89.96	11.519%	$100.3225	$100.32	$100.30	$100.30
Purchase #6	$85.98	6.433%	$91.5111	$91.51	$91.50	$91.50
Purchase #7	$215.42	10.619%	$238.2954	$238.30	$238.30	$238.30
7 purchase totals =	$935.49		$1,025.7997	$1,025.80	$1,025.75	$1,025.80