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	$80.47	10.150%	$88.6377	$88.64	$88.65	$88.60
Purchase #2	$169.51	9.339%	$185.3405	$185.34	$185.35	$185.30
Purchase #3	$224.69	8.703%	$244.2448	$244.24	$244.25	$244.20
Purchase #4	$31.39	4.293%	$32.7376	$32.74	$32.75	$32.70
Purchase #5	$177.73	7.454%	$190.978	$190.98	$191.00	$191.00
Purchase #6	$70.37	11.651%	$78.5688	$78.57	$78.55	$78.60
Purchase #7	$194.71	13.791%	$221.5625	$221.56	$221.55	$221.60
7 purchase totals =	$948.87		$1,042.0699	$1,042.07	$1,042.10	$1,042.00