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	$128.89	13.258%	$145.9782	$145.98	$146.00	$146.00
Purchase #2	$130.73	6.336%	$139.0131	$139.01	$139.00	$139.00
Purchase #3	$76.61	12.131%	$85.9036	$85.90	$85.90	$85.90
Purchase #4	$221.36	7.491%	$237.9421	$237.94	$237.95	$237.90
Purchase #5	$129.89	6.599%	$138.4614	$138.46	$138.45	$138.50
Purchase #6	$209.48	9.444%	$229.2633	$229.26	$229.25	$229.30
Purchase #7	$160.63	8.472%	$174.2386	$174.24	$174.25	$174.20
7 purchase totals =	$1,057.59		$1,150.8003	$1,150.79	$1,150.80	$1,150.80