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	$124.42	13.145%	$140.775	$140.78	$140.80	$140.80
Purchase #2	$247.90	5.171%	$260.7189	$260.72	$260.70	$260.70
Purchase #3	$150.46	9.399%	$164.6017	$164.60	$164.60	$164.60
Purchase #4	$169.48	7.360%	$181.9537	$181.95	$181.95	$182.00
Purchase #5	$107.83	9.567%	$118.1461	$118.15	$118.15	$118.10
Purchase #6	$73.34	12.261%	$82.3322	$82.33	$82.35	$82.30
Purchase #7	$62.75	10.489%	$69.3318	$69.33	$69.35	$69.30
7 purchase totals =	$936.18		$1,017.8594	$1,017.86	$1,017.90	$1,017.80