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	$138.58	4.112%	$144.2784	$144.28	$144.30	$144.30
Purchase #2	$84.25	6.244%	$89.5106	$89.51	$89.50	$89.50
Purchase #3	$77.61	11.762%	$86.7385	$86.74	$86.75	$86.70
Purchase #4	$23.80	10.665%	$26.3383	$26.34	$26.35	$26.30
Purchase #5	$152.82	7.601%	$164.4358	$164.44	$164.45	$164.40
Purchase #6	$35.89	3.673%	$37.2082	$37.21	$37.20	$37.20
Purchase #7	$166.38	7.206%	$178.3693	$178.37	$178.35	$178.40
7 purchase totals =	$679.33		$726.8791	$726.89	$726.90	$726.80