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	$67.64	3.832%	$70.232	$70.23	$70.25	$70.20
Purchase #2	$238.82	4.815%	$250.3192	$250.32	$250.30	$250.30
Purchase #3	$65.88	8.276%	$71.3322	$71.33	$71.35	$71.30
Purchase #4	$99.65	9.292%	$108.9095	$108.91	$108.90	$108.90
Purchase #5	$29.62	6.735%	$31.6149	$31.61	$31.60	$31.60
Purchase #6	$58.98	5.758%	$62.3761	$62.38	$62.40	$62.40
Purchase #7	$234.53	4.430%	$244.9197	$244.92	$244.90	$244.90
7 purchase totals =	$795.12		$839.7036	$839.70	$839.70	$839.60