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	$123.93	11.587%	$138.2898	$138.29	$138.30	$138.30
Purchase #2	$55.85	10.540%	$61.7366	$61.74	$61.75	$61.70
Purchase #3	$78.74	13.220%	$89.1494	$89.15	$89.15	$89.10
Purchase #4	$239.84	6.449%	$255.3073	$255.31	$255.30	$255.30
Purchase #5	$37.44	7.107%	$40.1009	$40.10	$40.10	$40.10
Purchase #6	$134.93	12.455%	$151.7355	$151.74	$151.75	$151.70
Purchase #7	$218.95	9.753%	$240.3042	$240.30	$240.30	$240.30
7 purchase totals =	$889.68		$976.6237	$976.63	$976.65	$976.50