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	$80.86	10.151%	$89.0681	$89.07	$89.05	$89.10
Purchase #2	$88.72	13.597%	$100.7833	$100.78	$100.80	$100.80
Purchase #3	$83.41	6.638%	$88.9468	$88.95	$88.95	$88.90
Purchase #4	$174.72	5.155%	$183.7268	$183.73	$183.75	$183.70
Purchase #5	$229.63	4.662%	$240.3354	$240.34	$240.35	$240.30
Purchase #6	$81.96	4.129%	$85.3441	$85.34	$85.35	$85.30
Purchase #7	$82.91	5.203%	$87.2238	$87.22	$87.20	$87.20
7 purchase totals =	$822.21		$875.4283	$875.43	$875.45	$875.30