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	$92.53	10.587%	$102.3262	$102.33	$102.35	$102.30
Purchase #2	$136.32	10.778%	$151.0126	$151.01	$151.00	$151.00
Purchase #3	$99.78	4.747%	$104.5166	$104.52	$104.50	$104.50
Purchase #4	$236.46	11.590%	$263.8657	$263.87	$263.85	$263.90
Purchase #5	$75.88	5.702%	$80.2067	$80.21	$80.20	$80.20
Purchase #6	$12.89	7.800%	$13.8954	$13.90	$13.90	$13.90
Purchase #7	$80.57	12.331%	$90.5051	$90.51	$90.50	$90.50
7 purchase totals =	$734.43		$806.3283	$806.35	$806.30	$806.30