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	$98.90	5.794%	$104.6303	$104.63	$104.65	$104.60
Purchase #2	$42.85	13.672%	$48.7085	$48.71	$48.70	$48.70
Purchase #3	$145.65	10.133%	$160.4087	$160.41	$160.40	$160.40
Purchase #4	$42.62	7.113%	$45.6516	$45.65	$45.65	$45.70
Purchase #5	$53.72	11.581%	$59.9413	$59.94	$59.95	$59.90
Purchase #6	$182.89	11.130%	$203.2457	$203.25	$203.25	$203.20
Purchase #7	$189.98	12.321%	$213.3874	$213.39	$213.40	$213.40
7 purchase totals =	$756.61		$835.9735	$835.98	$836.00	$835.90