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	$70.54	10.778%	$78.1428	$78.14	$78.15	$78.10
Purchase #2	$42.67	7.532%	$45.8839	$45.88	$45.90	$45.90
Purchase #3	$99.96	12.278%	$112.2331	$112.23	$112.25	$112.20
Purchase #4	$123.76	7.188%	$132.6559	$132.66	$132.65	$132.70
Purchase #5	$113.65	6.288%	$120.7963	$120.80	$120.80	$120.80
Purchase #6	$92.56	10.485%	$102.2649	$102.26	$102.25	$102.30
Purchase #7	$248.70	12.444%	$279.6482	$279.65	$279.65	$279.60
7 purchase totals =	$791.84		$871.6251	$871.62	$871.65	$871.60