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	$178.66	3.206%	$184.3878	$184.39	$184.40	$184.40
Purchase #2	$221.98	6.241%	$235.8338	$235.83	$235.85	$235.80
Purchase #3	$211.61	10.579%	$233.9962	$234.00	$234.00	$234.00
Purchase #4	$150.28	3.506%	$155.5488	$155.55	$155.55	$155.50
Purchase #5	$20.52	5.813%	$21.7128	$21.71	$21.70	$21.70
Purchase #6	$186.48	5.595%	$196.9136	$196.91	$196.90	$196.90
Purchase #7	$55.51	13.344%	$62.9173	$62.92	$62.90	$62.90
7 purchase totals =	$1,025.04		$1,091.3103	$1,091.31	$1,091.30	$1,091.20