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	$57.41	10.586%	$63.4874	$63.49	$63.50	$63.50
Purchase #2	$201.85	13.564%	$229.2289	$229.23	$229.25	$229.20
Purchase #3	$231.36	4.107%	$240.862	$240.86	$240.85	$240.90
Purchase #4	$79.47	8.241%	$86.0191	$86.02	$86.00	$86.00
Purchase #5	$11.54	10.807%	$12.7871	$12.79	$12.80	$12.80
Purchase #6	$143.27	6.115%	$152.031	$152.03	$152.05	$152.00
Purchase #7	$95.81	10.459%	$105.8308	$105.83	$105.85	$105.80
7 purchase totals =	$820.71		$890.2463	$890.25	$890.30	$890.20