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	$114.43	4.846%	$119.9753	$119.98	$120.00	$120.00
Purchase #2	$87.52	3.874%	$90.9105	$90.91	$90.90	$90.90
Purchase #3	$179.66	11.493%	$200.3083	$200.31	$200.30	$200.30
Purchase #4	$125.53	9.715%	$137.7252	$137.73	$137.75	$137.70
Purchase #5	$151.88	9.663%	$166.5562	$166.56	$166.55	$166.60
Purchase #6	$152.79	11.170%	$169.8566	$169.86	$169.85	$169.90
Purchase #7	$138.30	12.265%	$155.2625	$155.26	$155.25	$155.30
7 purchase totals =	$950.11		$1,040.5946	$1,040.61	$1,040.60	$1,040.70