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	$61.38	9.636%	$67.2946	$67.29	$67.30	$67.30
Purchase #2	$142.26	4.419%	$148.5465	$148.55	$148.55	$148.50
Purchase #3	$198.41	10.589%	$219.4196	$219.42	$219.40	$219.40
Purchase #4	$39.46	6.430%	$41.9973	$42.00	$42.00	$42.00
Purchase #5	$67.43	7.741%	$72.6498	$72.65	$72.65	$72.60
Purchase #6	$239.34	6.165%	$254.0953	$254.10	$254.10	$254.10
Purchase #7	$57.39	12.350%	$64.4777	$64.48	$64.50	$64.50
7 purchase totals =	$805.67		$868.4808	$868.49	$868.50	$868.40