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	$131.78	5.285%	$138.7446	$138.74	$138.75	$138.70
Purchase #2	$80.40	10.870%	$89.1395	$89.14	$89.15	$89.10
Purchase #3	$165.37	6.351%	$175.8726	$175.87	$175.85	$175.90
Purchase #4	$37.62	8.421%	$40.788	$40.79	$40.80	$40.80
Purchase #5	$135.99	10.531%	$150.3111	$150.31	$150.30	$150.30
Purchase #6	$212.43	7.135%	$227.5869	$227.59	$227.60	$227.60
Purchase #7	$164.90	5.477%	$173.9316	$173.93	$173.95	$173.90
7 purchase totals =	$928.49		$996.3743	$996.37	$996.40	$996.30