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	$131.88	6.653%	$140.654	$140.65	$140.65	$140.70
Purchase #2	$211.58	10.269%	$233.3072	$233.31	$233.30	$233.30
Purchase #3	$90.36	9.805%	$99.2198	$99.22	$99.20	$99.20
Purchase #4	$28.76	6.443%	$30.613	$30.61	$30.60	$30.60
Purchase #5	$224.60	5.314%	$236.5352	$236.54	$236.55	$236.50
Purchase #6	$132.75	5.427%	$139.9543	$139.95	$139.95	$140.00
Purchase #7	$94.53	9.833%	$103.8251	$103.83	$103.85	$103.80
7 purchase totals =	$914.46		$984.1086	$984.11	$984.10	$984.10