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	$135.95	9.809%	$149.2853	$149.29	$149.30	$149.30
Purchase #2	$75.28	13.656%	$85.5602	$85.56	$85.55	$85.60
Purchase #3	$118.91	4.245%	$123.9577	$123.96	$123.95	$124.00
Purchase #4	$93.61	10.315%	$103.2659	$103.27	$103.25	$103.30
Purchase #5	$242.27	5.599%	$255.8347	$255.83	$255.85	$255.80
Purchase #6	$148.28	7.469%	$159.355	$159.36	$159.35	$159.40
Purchase #7	$54.39	13.558%	$61.7642	$61.76	$61.75	$61.80
7 purchase totals =	$868.69		$939.0230	$939.03	$939.00	$939.20