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	$19.90	9.207%	$21.7322	$21.73	$21.75	$21.70
Purchase #2	$66.78	8.268%	$72.3014	$72.30	$72.30	$72.30
Purchase #3	$59.82	8.416%	$64.8545	$64.85	$64.85	$64.90
Purchase #4	$216.87	11.376%	$241.5411	$241.54	$241.55	$241.50
Purchase #5	$28.71	13.428%	$32.5652	$32.57	$32.55	$32.60
Purchase #6	$85.66	4.465%	$89.4847	$89.48	$89.50	$89.50
Purchase #7	$159.76	11.506%	$178.142	$178.14	$178.15	$178.10
7 purchase totals =	$637.50		$700.6211	$700.61	$700.65	$700.60