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	$26.53	11.149%	$29.4878	$29.49	$29.50	$29.50
Purchase #2	$212.33	8.270%	$229.8897	$229.89	$229.90	$229.90
Purchase #3	$79.69	11.734%	$89.0408	$89.04	$89.05	$89.00
Purchase #4	$243.40	11.556%	$271.5273	$271.53	$271.55	$271.50
Purchase #5	$71.89	13.266%	$81.4269	$81.43	$81.45	$81.40
Purchase #6	$220.66	12.846%	$249.006	$249.01	$249.00	$249.00
Purchase #7	$25.58	9.674%	$28.0546	$28.05	$28.05	$28.10
7 purchase totals =	$880.08		$978.4331	$978.44	$978.50	$978.40