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	$236.91	8.109%	$256.121	$256.12	$256.10	$256.10
Purchase #2	$16.89	10.179%	$18.6092	$18.61	$18.60	$18.60
Purchase #3	$45.33	11.722%	$50.6436	$50.64	$50.65	$50.60
Purchase #4	$155.79	7.748%	$167.8606	$167.86	$167.85	$167.90
Purchase #5	$176.30	8.864%	$191.9272	$191.93	$191.95	$191.90
Purchase #6	$106.55	12.835%	$120.2257	$120.23	$120.25	$120.20
Purchase #7	$120.61	13.516%	$136.9116	$136.91	$136.90	$136.90
7 purchase totals =	$858.38		$942.2989	$942.30	$942.30	$942.20