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	$139.93	6.228%	$148.6448	$148.64	$148.65	$148.60
Purchase #2	$170.47	11.768%	$190.5309	$190.53	$190.55	$190.50
Purchase #3	$73.31	5.727%	$77.5085	$77.51	$77.50	$77.50
Purchase #4	$96.53	4.575%	$100.9462	$100.95	$100.95	$100.90
Purchase #5	$5.48	7.170%	$5.8729	$5.87	$5.85	$5.90
Purchase #6	$96.73	7.141%	$103.6375	$103.64	$103.65	$103.60
Purchase #7	$235.48	12.740%	$265.4802	$265.48	$265.50	$265.50
7 purchase totals =	$817.93		$892.6210	$892.62	$892.65	$892.50