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	$170.79	8.736%	$185.7102	$185.71	$185.70	$185.70
Purchase #2	$169.42	11.524%	$188.944	$188.94	$188.95	$188.90
Purchase #3	$75.92	3.738%	$78.7579	$78.76	$78.75	$78.80
Purchase #4	$128.83	4.315%	$134.389	$134.39	$134.40	$134.40
Purchase #5	$227.72	10.821%	$252.3616	$252.36	$252.35	$252.40
Purchase #6	$78.67	4.187%	$81.9639	$81.96	$81.95	$82.00
Purchase #7	$82.63	3.307%	$85.3626	$85.36	$85.35	$85.40
7 purchase totals =	$933.98		$1,007.4892	$1,007.48	$1,007.45	$1,007.60