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	$154.89	8.796%	$168.5141	$168.51	$168.50	$168.50
Purchase #2	$131.31	11.495%	$146.4041	$146.40	$146.40	$146.40
Purchase #3	$38.97	8.627%	$42.3319	$42.33	$42.35	$42.30
Purchase #4	$86.38	11.516%	$96.3275	$96.33	$96.35	$96.30
Purchase #5	$69.86	5.394%	$73.6282	$73.63	$73.65	$73.60
Purchase #6	$75.37	9.305%	$82.3832	$82.38	$82.40	$82.40
Purchase #7	$239.56	11.797%	$267.8209	$267.82	$267.80	$267.80
7 purchase totals =	$796.34		$877.4099	$877.40	$877.45	$877.30