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	$37.53	13.507%	$42.5992	$42.60	$42.60	$42.60
Purchase #2	$50.59	10.478%	$55.8908	$55.89	$55.90	$55.90
Purchase #3	$209.31	13.635%	$237.8494	$237.85	$237.85	$237.80
Purchase #4	$81.42	12.361%	$91.4843	$91.48	$91.50	$91.50
Purchase #5	$100.27	12.116%	$112.4187	$112.42	$112.40	$112.40
Purchase #6	$208.71	5.261%	$219.6902	$219.69	$219.70	$219.70
Purchase #7	$198.40	9.736%	$217.7162	$217.72	$217.70	$217.70
7 purchase totals =	$886.23		$977.6488	$977.65	$977.65	$977.60