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	$90.56	7.618%	$97.4589	$97.46	$97.45	$97.50
Purchase #2	$126.28	4.482%	$131.9399	$131.94	$131.95	$131.90
Purchase #3	$93.32	6.799%	$99.6648	$99.66	$99.65	$99.70
Purchase #4	$163.37	8.704%	$177.5897	$177.59	$177.60	$177.60
Purchase #5	$53.43	8.656%	$58.0549	$58.05	$58.05	$58.10
Purchase #6	$89.44	11.846%	$100.0351	$100.04	$100.05	$100.00
Purchase #7	$19.58	9.150%	$21.3716	$21.37	$21.35	$21.40
7 purchase totals =	$635.98		$686.1149	$686.11	$686.10	$686.20