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	$117.28	6.120%	$124.4575	$124.46	$124.45	$124.50
Purchase #2	$220.50	7.267%	$236.5237	$236.52	$236.50	$236.50
Purchase #3	$134.85	5.755%	$142.6106	$142.61	$142.60	$142.60
Purchase #4	$152.75	11.383%	$170.1375	$170.14	$170.15	$170.10
Purchase #5	$101.83	9.824%	$111.8338	$111.83	$111.85	$111.80
Purchase #6	$83.81	6.713%	$89.4362	$89.44	$89.45	$89.40
Purchase #7	$37.79	13.818%	$43.0118	$43.01	$43.00	$43.00
7 purchase totals =	$848.81		$918.0111	$918.01	$918.00	$917.90