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	$186.56	6.343%	$198.3935	$198.39	$198.40	$198.40
Purchase #2	$38.75	7.542%	$41.6725	$41.67	$41.65	$41.70
Purchase #3	$195.87	6.756%	$209.103	$209.10	$209.10	$209.10
Purchase #4	$247.52	6.176%	$262.8068	$262.81	$262.80	$262.80
Purchase #5	$116.34	6.802%	$124.2534	$124.25	$124.25	$124.30
Purchase #6	$73.25	6.648%	$78.1197	$78.12	$78.10	$78.10
Purchase #7	$84.88	6.520%	$90.4142	$90.41	$90.40	$90.40
7 purchase totals =	$943.17		$1,004.7631	$1,004.75	$1,004.70	$1,004.80