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	$129.54	10.758%	$143.4759	$143.48	$143.50	$143.50
Purchase #2	$187.33	8.628%	$203.4928	$203.49	$203.50	$203.50
Purchase #3	$55.99	9.529%	$61.3253	$61.33	$61.35	$61.30
Purchase #4	$155.82	6.837%	$166.4734	$166.47	$166.45	$166.50
Purchase #5	$65.44	10.629%	$72.3956	$72.40	$72.40	$72.40
Purchase #6	$133.62	8.302%	$144.7131	$144.71	$144.70	$144.70
Purchase #7	$83.86	4.465%	$87.6043	$87.60	$87.60	$87.60
7 purchase totals =	$811.60		$879.4804	$879.48	$879.50	$879.50