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	$32.35	4.438%	$33.7857	$33.79	$33.80	$33.80
Purchase #2	$152.63	13.272%	$172.8871	$172.89	$172.90	$172.90
Purchase #3	$130.55	6.824%	$139.4587	$139.46	$139.45	$139.50
Purchase #4	$196.60	4.334%	$205.1206	$205.12	$205.10	$205.10
Purchase #5	$232.33	10.561%	$256.8664	$256.87	$256.85	$256.90
Purchase #6	$19.60	4.433%	$20.4689	$20.47	$20.45	$20.50
Purchase #7	$28.63	9.525%	$31.357	$31.36	$31.35	$31.40
7 purchase totals =	$792.69		$859.9444	$859.96	$859.90	$860.10