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	$80.41	3.612%	$83.3144	$83.31	$83.30	$83.30
Purchase #2	$67.66	11.622%	$75.5234	$75.52	$75.50	$75.50
Purchase #3	$131.96	9.700%	$144.7601	$144.76	$144.75	$144.80
Purchase #4	$31.30	11.335%	$34.8479	$34.85	$34.85	$34.80
Purchase #5	$85.66	3.540%	$88.6924	$88.69	$88.70	$88.70
Purchase #6	$99.71	4.833%	$104.529	$104.53	$104.55	$104.50
Purchase #7	$42.28	4.780%	$44.301	$44.30	$44.30	$44.30
7 purchase totals =	$538.98		$575.9682	$575.96	$575.95	$575.90