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	$158.80	6.515%	$169.1458	$169.15	$169.15	$169.10
Purchase #2	$134.30	4.159%	$139.8855	$139.89	$139.90	$139.90
Purchase #3	$216.27	11.146%	$240.3755	$240.38	$240.40	$240.40
Purchase #4	$97.62	5.627%	$103.1131	$103.11	$103.10	$103.10
Purchase #5	$215.39	13.794%	$245.1009	$245.10	$245.10	$245.10
Purchase #6	$7.60	3.850%	$7.8926	$7.89	$7.90	$7.90
Purchase #7	$37.91	8.710%	$41.212	$41.21	$41.20	$41.20
7 purchase totals =	$867.89		$946.7254	$946.73	$946.75	$946.70