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	$79.55	3.609%	$82.421	$82.42	$82.40	$82.40
Purchase #2	$5.34	6.124%	$5.667	$5.67	$5.65	$5.70
Purchase #3	$129.70	7.473%	$139.3925	$139.39	$139.40	$139.40
Purchase #4	$154.33	8.124%	$166.8678	$166.87	$166.85	$166.90
Purchase #5	$97.76	6.316%	$103.9345	$103.93	$103.95	$103.90
Purchase #6	$244.90	7.346%	$262.8904	$262.89	$262.90	$262.90
Purchase #7	$124.46	9.381%	$136.1356	$136.14	$136.15	$136.10
7 purchase totals =	$836.04		$897.3088	$897.31	$897.30	$897.30