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	$178.38	12.581%	$200.822	$200.82	$200.80	$200.80
Purchase #2	$156.46	6.224%	$166.1981	$166.20	$166.20	$166.20
Purchase #3	$72.29	8.614%	$78.5171	$78.52	$78.50	$78.50
Purchase #4	$38.69	5.512%	$40.8226	$40.82	$40.80	$40.80
Purchase #5	$196.56	4.794%	$205.9831	$205.98	$206.00	$206.00
Purchase #6	$193.75	10.620%	$214.3263	$214.33	$214.35	$214.30
Purchase #7	$22.36	13.337%	$25.3422	$25.34	$25.35	$25.30
7 purchase totals =	$858.49		$932.0114	$932.01	$932.00	$931.90