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	$105.44	7.673%	$113.5304	$113.53	$113.55	$113.50
Purchase #2	$171.68	11.715%	$191.7923	$191.79	$191.80	$191.80
Purchase #3	$38.54	5.711%	$40.741	$40.74	$40.75	$40.70
Purchase #4	$35.98	4.417%	$37.5692	$37.57	$37.55	$37.60
Purchase #5	$148.77	10.790%	$164.8223	$164.82	$164.80	$164.80
Purchase #6	$94.89	13.554%	$107.7514	$107.75	$107.75	$107.80
Purchase #7	$22.94	7.331%	$24.6217	$24.62	$24.60	$24.60
7 purchase totals =	$618.24		$680.8283	$680.82	$680.80	$680.80