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	$112.67	7.718%	$121.3659	$121.37	$121.35	$121.40
Purchase #2	$100.65	10.865%	$111.5856	$111.59	$111.60	$111.60
Purchase #3	$167.39	12.527%	$188.3589	$188.36	$188.35	$188.40
Purchase #4	$98.70	12.850%	$111.383	$111.38	$111.40	$111.40
Purchase #5	$138.99	4.720%	$145.5503	$145.55	$145.55	$145.60
Purchase #6	$104.96	3.118%	$108.2327	$108.23	$108.25	$108.20
Purchase #7	$67.25	5.819%	$71.1633	$71.16	$71.15	$71.20
7 purchase totals =	$790.61		$857.6397	$857.64	$857.65	$857.80