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	$6.73	6.367%	$7.1585	$7.16	$7.15	$7.20
Purchase #2	$74.38	12.410%	$83.6106	$83.61	$83.60	$83.60
Purchase #3	$243.74	8.151%	$263.6072	$263.61	$263.60	$263.60
Purchase #4	$39.37	10.342%	$43.4416	$43.44	$43.45	$43.40
Purchase #5	$206.78	8.339%	$224.0234	$224.02	$224.00	$224.00
Purchase #6	$46.45	3.597%	$48.1208	$48.12	$48.10	$48.10
Purchase #7	$69.55	4.235%	$72.4954	$72.50	$72.50	$72.50
7 purchase totals =	$687.00		$742.4575	$742.46	$742.40	$742.40