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	$6.81	8.495%	$7.3885	$7.39	$7.40	$7.40
Purchase #2	$147.98	5.164%	$155.6217	$155.62	$155.60	$155.60
Purchase #3	$186.68	12.726%	$210.4369	$210.44	$210.45	$210.40
Purchase #4	$95.62	6.138%	$101.4892	$101.49	$101.50	$101.50
Purchase #5	$121.72	12.794%	$137.2929	$137.29	$137.30	$137.30
Purchase #6	$99.92	12.205%	$112.1152	$112.12	$112.10	$112.10
Purchase #7	$118.48	7.646%	$127.539	$127.54	$127.55	$127.50
7 purchase totals =	$777.21		$851.8834	$851.89	$851.90	$851.80