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	$43.67	10.866%	$48.4152	$48.42	$48.40	$48.40
Purchase #2	$82.74	6.258%	$87.9179	$87.92	$87.90	$87.90
Purchase #3	$129.53	13.111%	$146.5127	$146.51	$146.50	$146.50
Purchase #4	$82.41	11.606%	$91.9745	$91.97	$91.95	$92.00
Purchase #5	$49.80	11.359%	$55.4568	$55.46	$55.45	$55.50
Purchase #6	$110.84	11.356%	$123.427	$123.43	$123.45	$123.40
Purchase #7	$76.79	5.366%	$80.9106	$80.91	$80.90	$80.90
7 purchase totals =	$575.78		$634.6147	$634.62	$634.55	$634.60