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	$209.72	7.826%	$226.1327	$226.13	$226.15	$226.10
Purchase #2	$197.47	12.171%	$221.5041	$221.50	$221.50	$221.50
Purchase #3	$238.83	6.304%	$253.8858	$253.89	$253.90	$253.90
Purchase #4	$55.40	7.394%	$59.4963	$59.50	$59.50	$59.50
Purchase #5	$213.62	7.213%	$229.0284	$229.03	$229.05	$229.00
Purchase #6	$232.63	8.156%	$251.6033	$251.60	$251.60	$251.60
Purchase #7	$72.93	8.244%	$78.9423	$78.94	$78.95	$78.90
7 purchase totals =	$1,220.60		$1,320.5929	$1,320.59	$1,320.65	$1,320.50