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	$81.35	11.288%	$90.5328	$90.53	$90.55	$90.50
Purchase #2	$247.69	8.431%	$268.5727	$268.57	$268.55	$268.60
Purchase #3	$89.29	11.714%	$99.7494	$99.75	$99.75	$99.70
Purchase #4	$182.48	6.597%	$194.5182	$194.52	$194.50	$194.50
Purchase #5	$185.40	13.133%	$209.7486	$209.75	$209.75	$209.70
Purchase #6	$66.94	6.722%	$71.4397	$71.44	$71.45	$71.40
Purchase #7	$37.81	12.597%	$42.5729	$42.57	$42.55	$42.60
7 purchase totals =	$890.96		$977.1343	$977.13	$977.10	$977.00