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	$71.96	12.279%	$80.796	$80.80	$80.80	$80.80
Purchase #2	$37.46	12.457%	$42.1264	$42.13	$42.15	$42.10
Purchase #3	$107.90	10.776%	$119.5273	$119.53	$119.55	$119.50
Purchase #4	$223.41	6.298%	$237.4804	$237.48	$237.50	$237.50
Purchase #5	$174.27	10.449%	$192.4795	$192.48	$192.50	$192.50
Purchase #6	$146.36	12.461%	$164.5979	$164.60	$164.60	$164.60
Purchase #7	$147.49	5.394%	$155.4456	$155.45	$155.45	$155.40
7 purchase totals =	$908.85		$992.4531	$992.47	$992.55	$992.40