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	$115.29	13.695%	$131.079	$131.08	$131.10	$131.10
Purchase #2	$47.26	12.340%	$53.0919	$53.09	$53.10	$53.10
Purchase #3	$82.82	9.729%	$90.8776	$90.88	$90.90	$90.90
Purchase #4	$32.99	9.117%	$35.9977	$36.00	$36.00	$36.00
Purchase #5	$151.35	4.562%	$158.2546	$158.25	$158.25	$158.30
Purchase #6	$91.40	4.270%	$95.3028	$95.30	$95.30	$95.30
Purchase #7	$199.56	8.686%	$216.8938	$216.89	$216.90	$216.90
7 purchase totals =	$720.67		$781.4974	$781.49	$781.55	$781.60