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	$68.32	4.187%	$71.1806	$71.18	$71.20	$71.20
Purchase #2	$121.81	13.196%	$137.884	$137.88	$137.90	$137.90
Purchase #3	$45.79	10.143%	$50.4345	$50.43	$50.45	$50.40
Purchase #4	$161.34	11.511%	$179.9118	$179.91	$179.90	$179.90
Purchase #5	$59.45	11.395%	$66.2243	$66.22	$66.20	$66.20
Purchase #6	$236.39	9.598%	$259.0787	$259.08	$259.10	$259.10
Purchase #7	$249.47	8.106%	$269.692	$269.69	$269.70	$269.70
7 purchase totals =	$942.57		$1,034.4059	$1,034.39	$1,034.45	$1,034.40