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	$11.86	5.672%	$12.5327	$12.53	$12.55	$12.50
Purchase #2	$89.45	12.830%	$100.9264	$100.93	$100.95	$100.90
Purchase #3	$140.88	7.702%	$151.7306	$151.73	$151.75	$151.70
Purchase #4	$86.95	10.646%	$96.2067	$96.21	$96.20	$96.20
Purchase #5	$73.76	13.179%	$83.4808	$83.48	$83.50	$83.50
Purchase #6	$139.92	7.404%	$150.2797	$150.28	$150.30	$150.30
Purchase #7	$18.81	12.775%	$21.213	$21.21	$21.20	$21.20
7 purchase totals =	$561.63		$616.3699	$616.37	$616.45	$616.30