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	$70.27	11.777%	$78.5457	$78.55	$78.55	$78.50
Purchase #2	$152.29	12.870%	$171.8897	$171.89	$171.90	$171.90
Purchase #3	$93.56	13.209%	$105.9183	$105.92	$105.90	$105.90
Purchase #4	$215.44	7.867%	$232.3887	$232.39	$232.40	$232.40
Purchase #5	$173.46	5.768%	$183.4652	$183.47	$183.45	$183.50
Purchase #6	$209.46	11.250%	$233.0243	$233.02	$233.00	$233.00
Purchase #7	$208.29	9.642%	$228.3733	$228.37	$228.35	$228.40
7 purchase totals =	$1,122.77		$1,233.6052	$1,233.61	$1,233.55	$1,233.60