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	$82.73	7.575%	$88.9968	$89.00	$89.00	$89.00
Purchase #2	$37.45	13.246%	$42.4106	$42.41	$42.40	$42.40
Purchase #3	$197.94	10.534%	$218.791	$218.79	$218.80	$218.80
Purchase #4	$190.61	11.593%	$212.7074	$212.71	$212.70	$212.70
Purchase #5	$86.84	4.429%	$90.6861	$90.69	$90.70	$90.70
Purchase #6	$49.52	4.329%	$51.6637	$51.66	$51.65	$51.70
Purchase #7	$212.59	3.405%	$219.8287	$219.83	$219.85	$219.80
7 purchase totals =	$857.68		$925.0843	$925.09	$925.10	$925.10