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	$177.27	10.676%	$196.1953	$196.20	$196.20	$196.20
Purchase #2	$107.51	5.400%	$113.3155	$113.32	$113.30	$113.30
Purchase #3	$192.83	4.198%	$200.925	$200.93	$200.95	$200.90
Purchase #4	$25.82	10.293%	$28.4777	$28.48	$28.50	$28.50
Purchase #5	$52.83	11.266%	$58.7818	$58.78	$58.80	$58.80
Purchase #6	$63.53	6.121%	$67.4187	$67.42	$67.40	$67.40
Purchase #7	$119.47	4.222%	$124.514	$124.51	$124.50	$124.50
7 purchase totals =	$739.26		$789.6280	$789.64	$789.65	$789.60