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	$80.91	3.125%	$83.4384	$83.44	$83.45	$83.40
Purchase #2	$181.37	13.759%	$206.3247	$206.32	$206.30	$206.30
Purchase #3	$132.35	10.497%	$146.2428	$146.24	$146.25	$146.20
Purchase #4	$90.62	4.166%	$94.3952	$94.40	$94.40	$94.40
Purchase #5	$69.93	12.715%	$78.8216	$78.82	$78.80	$78.80
Purchase #6	$125.74	12.466%	$141.4147	$141.41	$141.40	$141.40
Purchase #7	$17.85	11.846%	$19.9645	$19.96	$19.95	$20.00
7 purchase totals =	$698.77		$770.6019	$770.59	$770.55	$770.50