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	$234.81	13.543%	$266.6103	$266.61	$266.60	$266.60
Purchase #2	$25.63	13.570%	$29.108	$29.11	$29.10	$29.10
Purchase #3	$151.87	13.514%	$172.3937	$172.39	$172.40	$172.40
Purchase #4	$170.45	5.841%	$180.406	$180.41	$180.40	$180.40
Purchase #5	$187.34	6.443%	$199.4103	$199.41	$199.40	$199.40
Purchase #6	$104.37	5.281%	$109.8818	$109.88	$109.90	$109.90
Purchase #7	$239.79	12.602%	$270.0083	$270.01	$270.00	$270.00
7 purchase totals =	$1,114.26		$1,227.8184	$1,227.82	$1,227.80	$1,227.80