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	$177.53	4.559%	$185.6236	$185.62	$185.60	$185.60
Purchase #2	$140.91	6.640%	$150.2664	$150.27	$150.25	$150.30
Purchase #3	$218.98	9.421%	$239.6101	$239.61	$239.60	$239.60
Purchase #4	$179.26	6.769%	$191.3941	$191.39	$191.40	$191.40
Purchase #5	$92.76	7.174%	$99.4146	$99.41	$99.40	$99.40
Purchase #6	$37.95	4.187%	$39.539	$39.54	$39.55	$39.50
Purchase #7	$12.40	6.398%	$13.1934	$13.19	$13.20	$13.20
7 purchase totals =	$859.79		$919.0412	$919.03	$919.00	$919.00