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	$245.30	10.386%	$270.7769	$270.78	$270.80	$270.80
Purchase #2	$175.70	11.576%	$196.039	$196.04	$196.05	$196.00
Purchase #3	$174.31	12.403%	$195.9297	$195.93	$195.95	$195.90
Purchase #4	$194.90	10.126%	$214.6356	$214.64	$214.65	$214.60
Purchase #5	$91.41	3.441%	$94.5554	$94.56	$94.55	$94.60
Purchase #6	$126.78	8.780%	$137.9113	$137.91	$137.90	$137.90
Purchase #7	$54.67	12.413%	$61.4562	$61.46	$61.45	$61.50
7 purchase totals =	$1,063.07		$1,171.3041	$1,171.32	$1,171.35	$1,171.30