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	$122.63	13.684%	$139.4107	$139.41	$139.40	$139.40
Purchase #2	$243.45	4.446%	$254.2738	$254.27	$254.25	$254.30
Purchase #3	$183.27	3.753%	$190.1481	$190.15	$190.15	$190.10
Purchase #4	$71.91	9.237%	$78.5523	$78.55	$78.55	$78.60
Purchase #5	$85.75	8.402%	$92.9547	$92.95	$92.95	$93.00
Purchase #6	$211.65	6.589%	$225.5956	$225.60	$225.60	$225.60
Purchase #7	$11.61	10.682%	$12.8502	$12.85	$12.85	$12.90
7 purchase totals =	$930.27		$993.7854	$993.78	$993.75	$993.90