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	$30.82	12.407%	$34.6438	$34.64	$34.65	$34.60
Purchase #2	$161.98	8.595%	$175.9022	$175.90	$175.90	$175.90
Purchase #3	$166.67	11.225%	$185.3787	$185.38	$185.40	$185.40
Purchase #4	$96.33	3.195%	$99.4077	$99.41	$99.40	$99.40
Purchase #5	$80.95	8.704%	$87.9959	$88.00	$88.00	$88.00
Purchase #6	$231.44	8.168%	$250.344	$250.34	$250.35	$250.30
Purchase #7	$112.96	13.260%	$127.9385	$127.94	$127.95	$127.90
7 purchase totals =	$881.15		$961.6108	$961.61	$961.65	$961.50