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	$71.93	8.674%	$78.1692	$78.17	$78.15	$78.20
Purchase #2	$249.41	10.287%	$275.0668	$275.07	$275.05	$275.10
Purchase #3	$128.50	8.850%	$139.8723	$139.87	$139.85	$139.90
Purchase #4	$185.59	13.729%	$211.0697	$211.07	$211.05	$211.10
Purchase #5	$200.85	3.864%	$208.6108	$208.61	$208.60	$208.60
Purchase #6	$113.59	10.866%	$125.9327	$125.93	$125.95	$125.90
Purchase #7	$97.39	6.293%	$103.5188	$103.52	$103.50	$103.50
7 purchase totals =	$1,047.26		$1,142.2403	$1,142.24	$1,142.15	$1,142.30