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	$55.57	7.722%	$59.8611	$59.86	$59.85	$59.90
Purchase #2	$76.96	13.725%	$87.5228	$87.52	$87.50	$87.50
Purchase #3	$246.48	4.730%	$258.1385	$258.14	$258.15	$258.10
Purchase #4	$27.72	13.249%	$31.3926	$31.39	$31.40	$31.40
Purchase #5	$65.89	12.736%	$74.2818	$74.28	$74.30	$74.30
Purchase #6	$89.40	9.802%	$98.163	$98.16	$98.15	$98.20
Purchase #7	$58.64	10.440%	$64.762	$64.76	$64.75	$64.80
7 purchase totals =	$620.66		$674.1218	$674.11	$674.10	$674.20