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	$194.94	13.827%	$221.8944	$221.89	$221.90	$221.90
Purchase #2	$57.73	3.175%	$59.5629	$59.56	$59.55	$59.60
Purchase #3	$239.25	11.723%	$267.2973	$267.30	$267.30	$267.30
Purchase #4	$135.53	4.276%	$141.3253	$141.33	$141.35	$141.30
Purchase #5	$123.90	6.758%	$132.2732	$132.27	$132.25	$132.30
Purchase #6	$233.80	9.434%	$255.8567	$255.86	$255.85	$255.90
Purchase #7	$104.58	7.792%	$112.7289	$112.73	$112.75	$112.70
7 purchase totals =	$1,089.73		$1,190.9387	$1,190.94	$1,190.95	$1,191.00