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	$72.55	12.174%	$81.3822	$81.38	$81.40	$81.40
Purchase #2	$68.59	5.642%	$72.4598	$72.46	$72.45	$72.50
Purchase #3	$236.26	9.473%	$258.6409	$258.64	$258.65	$258.60
Purchase #4	$10.84	10.139%	$11.9391	$11.94	$11.95	$11.90
Purchase #5	$141.45	6.123%	$150.111	$150.11	$150.10	$150.10
Purchase #6	$243.96	6.403%	$259.5808	$259.58	$259.60	$259.60
Purchase #7	$235.70	9.234%	$257.4645	$257.46	$257.45	$257.50
7 purchase totals =	$1,009.35		$1,091.5783	$1,091.57	$1,091.60	$1,091.60