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	$37.98	5.366%	$40.018	$40.02	$40.00	$40.00
Purchase #2	$239.61	9.838%	$263.1828	$263.18	$263.20	$263.20
Purchase #3	$169.35	9.663%	$185.7143	$185.71	$185.70	$185.70
Purchase #4	$77.56	11.344%	$86.3584	$86.36	$86.35	$86.40
Purchase #5	$72.53	8.838%	$78.9402	$78.94	$78.95	$78.90
Purchase #6	$138.98	12.527%	$156.39	$156.39	$156.40	$156.40
Purchase #7	$146.90	5.341%	$154.7459	$154.75	$154.75	$154.70
7 purchase totals =	$882.91		$965.3496	$965.35	$965.35	$965.30