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	$100.81	5.353%	$106.2064	$106.21	$106.20	$106.20
Purchase #2	$103.56	8.282%	$112.1368	$112.14	$112.15	$112.10
Purchase #3	$85.30	11.810%	$95.3739	$95.37	$95.35	$95.40
Purchase #4	$35.78	7.110%	$38.324	$38.32	$38.30	$38.30
Purchase #5	$168.25	13.425%	$190.8376	$190.84	$190.85	$190.80
Purchase #6	$212.51	6.304%	$225.9066	$225.91	$225.90	$225.90
Purchase #7	$61.36	9.234%	$67.026	$67.03	$67.05	$67.00
7 purchase totals =	$767.57		$835.8113	$835.82	$835.80	$835.70