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	$179.65	10.448%	$198.4198	$198.42	$198.40	$198.40
Purchase #2	$169.46	12.207%	$190.146	$190.15	$190.15	$190.10
Purchase #3	$86.86	12.554%	$97.7644	$97.76	$97.75	$97.80
Purchase #4	$93.94	5.865%	$99.4496	$99.45	$99.45	$99.40
Purchase #5	$43.55	13.114%	$49.2611	$49.26	$49.25	$49.30
Purchase #6	$21.89	13.862%	$24.9244	$24.92	$24.90	$24.90
Purchase #7	$174.93	9.406%	$191.3839	$191.38	$191.40	$191.40
7 purchase totals =	$770.28		$851.3492	$851.34	$851.30	$851.30