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	$117.47	8.558%	$127.5231	$127.52	$127.50	$127.50
Purchase #2	$147.40	12.520%	$165.8545	$165.85	$165.85	$165.90
Purchase #3	$51.31	12.488%	$57.7176	$57.72	$57.70	$57.70
Purchase #4	$238.47	4.644%	$249.5445	$249.54	$249.55	$249.50
Purchase #5	$94.75	5.511%	$99.9717	$99.97	$99.95	$100.00
Purchase #6	$169.71	4.757%	$177.7831	$177.78	$177.80	$177.80
Purchase #7	$171.73	12.861%	$193.8162	$193.82	$193.80	$193.80
7 purchase totals =	$990.84		$1,072.2107	$1,072.20	$1,072.15	$1,072.20