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	$37.55	6.664%	$40.0523	$40.05	$40.05	$40.10
Purchase #2	$159.47	12.465%	$179.3479	$179.35	$179.35	$179.30
Purchase #3	$149.92	11.535%	$167.2133	$167.21	$167.20	$167.20
Purchase #4	$225.49	10.783%	$249.8046	$249.80	$249.80	$249.80
Purchase #5	$94.92	6.560%	$101.1468	$101.15	$101.15	$101.10
Purchase #6	$185.86	5.815%	$196.6678	$196.67	$196.65	$196.70
Purchase #7	$213.85	9.503%	$234.1722	$234.17	$234.15	$234.20
7 purchase totals =	$1,067.06		$1,168.4049	$1,168.40	$1,168.35	$1,168.40