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	$37.62	4.836%	$39.4393	$39.44	$39.45	$39.40
Purchase #2	$116.36	3.874%	$120.8678	$120.87	$120.85	$120.90
Purchase #3	$173.25	9.513%	$189.7313	$189.73	$189.75	$189.70
Purchase #4	$223.84	12.228%	$251.2112	$251.21	$251.20	$251.20
Purchase #5	$117.63	13.823%	$133.89	$133.89	$133.90	$133.90
Purchase #6	$172.43	5.305%	$181.5774	$181.58	$181.60	$181.60
Purchase #7	$82.42	9.665%	$90.3859	$90.39	$90.40	$90.40
7 purchase totals =	$923.55		$1,007.1029	$1,007.11	$1,007.15	$1,007.10