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	$215.58	11.736%	$240.8805	$240.88	$240.90	$240.90
Purchase #2	$29.91	13.190%	$33.8551	$33.86	$33.85	$33.90
Purchase #3	$97.89	9.301%	$106.9947	$106.99	$107.00	$107.00
Purchase #4	$157.57	7.472%	$169.3436	$169.34	$169.35	$169.30
Purchase #5	$56.88	4.271%	$59.3093	$59.31	$59.30	$59.30
Purchase #6	$79.70	13.442%	$90.4133	$90.41	$90.40	$90.40
Purchase #7	$141.69	7.187%	$151.8733	$151.87	$151.85	$151.90
7 purchase totals =	$779.22		$852.6698	$852.66	$852.65	$852.70