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	$77.66	5.700%	$82.0866	$82.09	$82.10	$82.10
Purchase #2	$242.73	3.662%	$251.6188	$251.62	$251.60	$251.60
Purchase #3	$193.69	3.596%	$200.6551	$200.66	$200.65	$200.70
Purchase #4	$184.36	6.356%	$196.0779	$196.08	$196.10	$196.10
Purchase #5	$242.66	9.551%	$265.8365	$265.84	$265.85	$265.80
Purchase #6	$201.89	13.187%	$228.5132	$228.51	$228.50	$228.50
Purchase #7	$59.63	5.319%	$62.8017	$62.80	$62.80	$62.80
7 purchase totals =	$1,202.62		$1,287.5898	$1,287.60	$1,287.60	$1,287.60