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	$47.57	11.839%	$53.2018	$53.20	$53.20	$53.20
Purchase #2	$52.51	9.181%	$57.3309	$57.33	$57.35	$57.30
Purchase #3	$52.85	12.667%	$59.5445	$59.54	$59.55	$59.50
Purchase #4	$67.90	6.346%	$72.2089	$72.21	$72.20	$72.20
Purchase #5	$102.50	5.720%	$108.363	$108.36	$108.35	$108.40
Purchase #6	$84.69	8.331%	$91.7455	$91.75	$91.75	$91.70
Purchase #7	$99.94	3.595%	$103.5328	$103.53	$103.55	$103.50
7 purchase totals =	$507.96		$545.9274	$545.92	$545.95	$545.80