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	$91.98	9.264%	$100.501	$100.50	$100.50	$100.50
Purchase #2	$46.60	13.211%	$52.7563	$52.76	$52.75	$52.80
Purchase #3	$172.38	13.261%	$195.2393	$195.24	$195.25	$195.20
Purchase #4	$88.95	8.637%	$96.6326	$96.63	$96.65	$96.60
Purchase #5	$195.35	7.249%	$209.5109	$209.51	$209.50	$209.50
Purchase #6	$92.79	13.451%	$105.2712	$105.27	$105.25	$105.30
Purchase #7	$77.77	13.450%	$88.2301	$88.23	$88.25	$88.20
7 purchase totals =	$765.82		$848.1414	$848.14	$848.15	$848.10