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	$123.34	12.853%	$139.1929	$139.19	$139.20	$139.20
Purchase #2	$177.69	7.138%	$190.3735	$190.37	$190.35	$190.40
Purchase #3	$160.36	12.735%	$180.7818	$180.78	$180.80	$180.80
Purchase #4	$35.94	10.583%	$39.7435	$39.74	$39.75	$39.70
Purchase #5	$244.80	7.685%	$263.6129	$263.61	$263.60	$263.60
Purchase #6	$84.52	6.236%	$89.7907	$89.79	$89.80	$89.80
Purchase #7	$140.70	10.519%	$155.5002	$155.50	$155.50	$155.50
7 purchase totals =	$967.35		$1,058.9955	$1,058.98	$1,059.00	$1,059.00