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	$155.41	11.364%	$173.0708	$173.07	$173.05	$173.10
Purchase #2	$115.61	6.475%	$123.0957	$123.10	$123.10	$123.10
Purchase #3	$236.83	11.190%	$263.3313	$263.33	$263.35	$263.30
Purchase #4	$144.28	7.266%	$154.7634	$154.76	$154.75	$154.80
Purchase #5	$68.28	7.597%	$73.4672	$73.47	$73.45	$73.50
Purchase #6	$148.55	8.683%	$161.4486	$161.45	$161.45	$161.40
Purchase #7	$48.50	12.814%	$54.7148	$54.71	$54.70	$54.70
7 purchase totals =	$917.46		$1,003.8918	$1,003.89	$1,003.85	$1,003.90