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	$74.77	4.708%	$78.2902	$78.29	$78.30	$78.30
Purchase #2	$86.78	3.356%	$89.6923	$89.69	$89.70	$89.70
Purchase #3	$10.94	7.646%	$11.7765	$11.78	$11.80	$11.80
Purchase #4	$141.41	5.635%	$149.3785	$149.38	$149.40	$149.40
Purchase #5	$45.87	13.369%	$52.0024	$52.00	$52.00	$52.00
Purchase #6	$220.31	10.302%	$243.0063	$243.01	$243.00	$243.00
Purchase #7	$43.54	13.245%	$49.3069	$49.31	$49.30	$49.30
7 purchase totals =	$623.62		$673.4531	$673.46	$673.50	$673.50