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	$69.32	8.701%	$75.3515	$75.35	$75.35	$75.40
Purchase #2	$90.98	9.759%	$99.8587	$99.86	$99.85	$99.90
Purchase #3	$40.61	13.817%	$46.2211	$46.22	$46.20	$46.20
Purchase #4	$107.47	12.474%	$120.8758	$120.88	$120.90	$120.90
Purchase #5	$167.67	13.671%	$190.5922	$190.59	$190.60	$190.60
Purchase #6	$162.59	3.490%	$168.2644	$168.26	$168.25	$168.30
Purchase #7	$72.52	13.521%	$82.3254	$82.33	$82.35	$82.30
7 purchase totals =	$711.16		$783.4891	$783.49	$783.50	$783.60