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	$72.34	7.868%	$78.0317	$78.03	$78.05	$78.00
Purchase #2	$166.52	11.522%	$185.7064	$185.71	$185.70	$185.70
Purchase #3	$8.69	4.446%	$9.0764	$9.08	$9.10	$9.10
Purchase #4	$108.72	7.260%	$116.6131	$116.61	$116.60	$116.60
Purchase #5	$40.36	4.812%	$42.3021	$42.30	$42.30	$42.30
Purchase #6	$95.42	13.299%	$108.1099	$108.11	$108.10	$108.10
Purchase #7	$147.72	12.218%	$165.7684	$165.77	$165.75	$165.80
7 purchase totals =	$639.77		$705.6080	$705.61	$705.60	$705.60