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	$34.81	8.814%	$37.8782	$37.88	$37.90	$37.90
Purchase #2	$65.74	10.762%	$72.8149	$72.81	$72.80	$72.80
Purchase #3	$162.37	6.174%	$172.3947	$172.39	$172.40	$172.40
Purchase #4	$37.33	13.348%	$42.3128	$42.31	$42.30	$42.30
Purchase #5	$222.42	6.450%	$236.7661	$236.77	$236.75	$236.80
Purchase #6	$161.63	11.378%	$180.0203	$180.02	$180.00	$180.00
Purchase #7	$141.89	13.624%	$161.2211	$161.22	$161.20	$161.20
7 purchase totals =	$826.19		$903.4081	$903.40	$903.35	$903.40