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	10.573%	$7.53	$7.53	$7.55	$7.50
Purchase #2	$61.46	11.178%	$68.33	$68.33	$68.35	$68.30
Purchase #3	$232.88	6.621%	$248.299	$248.30	$248.30	$248.30
Purchase #4	$238.62	9.596%	$261.518	$261.52	$261.50	$261.50
Purchase #5	$220.44	9.526%	$241.4391	$241.44	$241.45	$241.40
Purchase #6	$85.87	5.239%	$90.3687	$90.37	$90.35	$90.40
Purchase #7	$244.39	7.342%	$262.3331	$262.33	$262.35	$262.30
7 purchase totals =	$1,090.47		$1,179.8179	$1,179.82	$1,179.85	$1,179.70