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	$244.30	6.634%	$260.5069	$260.51	$260.50	$260.50
Purchase #2	$26.50	7.315%	$28.4385	$28.44	$28.45	$28.40
Purchase #3	$88.54	13.518%	$100.5088	$100.51	$100.50	$100.50
Purchase #4	$104.56	5.187%	$109.9835	$109.98	$110.00	$110.00
Purchase #5	$67.84	5.484%	$71.5603	$71.56	$71.55	$71.60
Purchase #6	$92.62	10.827%	$102.648	$102.65	$102.65	$102.60
Purchase #7	$199.50	8.457%	$216.3717	$216.37	$216.35	$216.40
7 purchase totals =	$823.86		$890.0177	$890.02	$890.00	$890.00