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	$69.36	3.628%	$71.8764	$71.88	$71.90	$71.90
Purchase #2	$20.29	3.659%	$21.0324	$21.03	$21.05	$21.00
Purchase #3	$139.79	6.513%	$148.8945	$148.89	$148.90	$148.90
Purchase #4	$54.29	10.237%	$59.8477	$59.85	$59.85	$59.80
Purchase #5	$157.81	12.166%	$177.0092	$177.01	$177.00	$177.00
Purchase #6	$145.86	7.311%	$156.5238	$156.52	$156.50	$156.50
Purchase #7	$145.73	6.442%	$155.1179	$155.12	$155.10	$155.10
7 purchase totals =	$733.13		$790.3019	$790.30	$790.30	$790.20