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	$150.93	10.701%	$167.081	$167.08	$167.10	$167.10
Purchase #2	$192.70	8.727%	$209.5169	$209.52	$209.50	$209.50
Purchase #3	$93.32	7.220%	$100.0577	$100.06	$100.05	$100.10
Purchase #4	$216.53	12.483%	$243.5594	$243.56	$243.55	$243.60
Purchase #5	$88.95	8.188%	$96.2332	$96.23	$96.25	$96.20
Purchase #6	$84.45	12.333%	$94.8652	$94.87	$94.85	$94.90
Purchase #7	$226.41	12.702%	$255.1686	$255.17	$255.15	$255.20
7 purchase totals =	$1,053.29		$1,166.4820	$1,166.49	$1,166.45	$1,166.60