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	$127.33	9.780%	$139.7829	$139.78	$139.80	$139.80
Purchase #2	$167.36	3.208%	$172.7289	$172.73	$172.75	$172.70
Purchase #3	$218.65	3.200%	$225.6468	$225.65	$225.65	$225.60
Purchase #4	$150.33	7.193%	$161.1432	$161.14	$161.15	$161.10
Purchase #5	$84.98	4.141%	$88.499	$88.50	$88.50	$88.50
Purchase #6	$88.50	12.166%	$99.2669	$99.27	$99.25	$99.30
Purchase #7	$223.81	12.834%	$252.5338	$252.53	$252.55	$252.50
7 purchase totals =	$1,060.96		$1,139.6015	$1,139.60	$1,139.65	$1,139.50