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	$120.55	8.757%	$131.1066	$131.11	$131.10	$131.10
Purchase #2	$109.75	3.826%	$113.949	$113.95	$113.95	$113.90
Purchase #3	$75.50	4.664%	$79.0213	$79.02	$79.00	$79.00
Purchase #4	$83.43	9.765%	$91.5769	$91.58	$91.60	$91.60
Purchase #5	$52.56	13.172%	$59.4832	$59.48	$59.50	$59.50
Purchase #6	$32.44	8.260%	$35.1195	$35.12	$35.10	$35.10
Purchase #7	$159.60	6.264%	$169.5973	$169.60	$169.60	$169.60
7 purchase totals =	$633.83		$679.8538	$679.86	$679.85	$679.80