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	$228.87	7.701%	$246.4953	$246.50	$246.50	$246.50
Purchase #2	$104.90	13.660%	$119.2293	$119.23	$119.25	$119.20
Purchase #3	$95.73	10.355%	$105.6428	$105.64	$105.65	$105.60
Purchase #4	$130.35	9.233%	$142.3852	$142.39	$142.40	$142.40
Purchase #5	$139.94	10.850%	$155.1235	$155.12	$155.10	$155.10
Purchase #6	$221.96	7.661%	$238.9644	$238.96	$238.95	$239.00
Purchase #7	$78.98	11.429%	$88.0066	$88.01	$88.00	$88.00
7 purchase totals =	$1,000.73		$1,095.8471	$1,095.85	$1,095.85	$1,095.80