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	$245.57	12.530%	$276.3399	$276.34	$276.35	$276.30
Purchase #2	$105.28	3.655%	$109.128	$109.13	$109.15	$109.10
Purchase #3	$32.45	12.179%	$36.4021	$36.40	$36.40	$36.40
Purchase #4	$139.33	6.420%	$148.275	$148.28	$148.30	$148.30
Purchase #5	$101.75	11.493%	$113.4441	$113.44	$113.45	$113.40
Purchase #6	$76.69	4.746%	$80.3297	$80.33	$80.35	$80.30
Purchase #7	$227.78	12.510%	$256.2753	$256.28	$256.30	$256.30
7 purchase totals =	$928.85		$1,020.1941	$1,020.20	$1,020.30	$1,020.10