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	$35.42	10.739%	$39.2238	$39.22	$39.20	$39.20
Purchase #2	$12.68	6.831%	$13.5462	$13.55	$13.55	$13.50
Purchase #3	$81.98	10.145%	$90.2969	$90.30	$90.30	$90.30
Purchase #4	$53.37	5.834%	$56.4836	$56.48	$56.50	$56.50
Purchase #5	$164.86	4.142%	$171.6885	$171.69	$171.70	$171.70
Purchase #6	$41.86	3.222%	$43.2087	$43.21	$43.20	$43.20
Purchase #7	$165.38	13.365%	$187.483	$187.48	$187.50	$187.50
7 purchase totals =	$555.55		$601.9307	$601.93	$601.95	$601.90