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	$125.84	9.451%	$137.7331	$137.73	$137.75	$137.70
Purchase #2	$160.83	6.473%	$171.2405	$171.24	$171.25	$171.20
Purchase #3	$92.99	11.203%	$103.4077	$103.41	$103.40	$103.40
Purchase #4	$151.78	7.255%	$162.7916	$162.79	$162.80	$162.80
Purchase #5	$87.37	4.639%	$91.4231	$91.42	$91.40	$91.40
Purchase #6	$118.72	4.785%	$124.4008	$124.40	$124.40	$124.40
Purchase #7	$72.41	11.139%	$80.4757	$80.48	$80.50	$80.50
7 purchase totals =	$809.94		$871.4725	$871.47	$871.50	$871.40