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	$154.71	7.298%	$166.0007	$166.00	$166.00	$166.00
Purchase #2	$53.51	4.317%	$55.82	$55.82	$55.80	$55.80
Purchase #3	$119.45	11.304%	$132.9526	$132.95	$132.95	$133.00
Purchase #4	$95.30	4.653%	$99.7343	$99.73	$99.75	$99.70
Purchase #5	$98.61	5.280%	$103.8166	$103.82	$103.80	$103.80
Purchase #6	$249.67	13.684%	$283.8348	$283.83	$283.85	$283.80
Purchase #7	$86.28	11.440%	$96.1504	$96.15	$96.15	$96.20
7 purchase totals =	$857.53		$938.3094	$938.30	$938.30	$938.30