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	$46.93	4.190%	$48.8964	$48.90	$48.90	$48.90
Purchase #2	$78.53	13.380%	$89.0373	$89.04	$89.05	$89.00
Purchase #3	$150.68	10.272%	$166.1578	$166.16	$166.15	$166.20
Purchase #4	$69.85	5.199%	$73.4815	$73.48	$73.50	$73.50
Purchase #5	$136.51	6.684%	$145.6343	$145.63	$145.65	$145.60
Purchase #6	$91.77	3.749%	$95.2105	$95.21	$95.20	$95.20
Purchase #7	$19.28	7.816%	$20.7869	$20.79	$20.80	$20.80
7 purchase totals =	$593.55		$639.2047	$639.21	$639.25	$639.20