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	$85.76	5.282%	$90.2898	$90.29	$90.30	$90.30
Purchase #2	$29.27	8.132%	$31.6502	$31.65	$31.65	$31.70
Purchase #3	$127.90	3.168%	$131.9519	$131.95	$131.95	$132.00
Purchase #4	$31.53	3.802%	$32.7288	$32.73	$32.75	$32.70
Purchase #5	$76.75	13.704%	$87.2678	$87.27	$87.25	$87.30
Purchase #6	$53.91	11.140%	$59.9156	$59.92	$59.90	$59.90
Purchase #7	$201.95	8.106%	$218.3201	$218.32	$218.30	$218.30
7 purchase totals =	$607.07		$652.1242	$652.13	$652.10	$652.20