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	$74.59	13.376%	$84.5672	$84.57	$84.55	$84.60
Purchase #2	$48.51	3.618%	$50.2651	$50.27	$50.25	$50.30
Purchase #3	$152.92	8.406%	$165.7745	$165.77	$165.75	$165.80
Purchase #4	$38.78	13.249%	$43.918	$43.92	$43.90	$43.90
Purchase #5	$239.86	3.215%	$247.5715	$247.57	$247.55	$247.60
Purchase #6	$184.53	12.843%	$208.2292	$208.23	$208.25	$208.20
Purchase #7	$197.98	10.541%	$218.8491	$218.85	$218.85	$218.80
7 purchase totals =	$937.17		$1,019.1746	$1,019.18	$1,019.10	$1,019.20