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	$238.35	3.320%	$246.2632	$246.26	$246.25	$246.30
Purchase #2	$80.55	6.281%	$85.6093	$85.61	$85.60	$85.60
Purchase #3	$227.50	4.299%	$237.2802	$237.28	$237.30	$237.30
Purchase #4	$89.33	12.609%	$100.5936	$100.59	$100.60	$100.60
Purchase #5	$170.48	10.587%	$188.5287	$188.53	$188.55	$188.50
Purchase #6	$57.41	13.275%	$65.0312	$65.03	$65.05	$65.00
Purchase #7	$234.53	10.675%	$259.5661	$259.57	$259.55	$259.60
7 purchase totals =	$1,098.15		$1,182.8723	$1,182.87	$1,182.90	$1,182.90