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	$94.66	9.724%	$103.8647	$103.86	$103.85	$103.90
Purchase #2	$151.58	12.127%	$169.9621	$169.96	$169.95	$170.00
Purchase #3	$72.50	7.592%	$78.0042	$78.00	$78.00	$78.00
Purchase #4	$230.63	5.256%	$242.7519	$242.75	$242.75	$242.80
Purchase #5	$124.33	11.859%	$139.0743	$139.07	$139.05	$139.10
Purchase #6	$146.36	13.786%	$166.5372	$166.54	$166.55	$166.50
Purchase #7	$175.83	8.862%	$191.4121	$191.41	$191.40	$191.40
7 purchase totals =	$995.89		$1,091.6065	$1,091.59	$1,091.55	$1,091.70