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	$78.89	4.269%	$82.2578	$82.26	$82.25	$82.30
Purchase #2	$247.96	13.359%	$281.085	$281.09	$281.10	$281.10
Purchase #3	$157.29	9.114%	$171.6254	$171.63	$171.65	$171.60
Purchase #4	$134.32	6.578%	$143.1556	$143.16	$143.15	$143.20
Purchase #5	$80.76	4.459%	$84.3611	$84.36	$84.35	$84.40
Purchase #6	$139.33	6.491%	$148.3739	$148.37	$148.35	$148.40
Purchase #7	$78.98	8.581%	$85.7573	$85.76	$85.75	$85.80
7 purchase totals =	$917.53		$996.6161	$996.63	$996.60	$996.80