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	$49.47	6.289%	$52.5812	$52.58	$52.60	$52.60
Purchase #2	$220.35	12.816%	$248.5901	$248.59	$248.60	$248.60
Purchase #3	$59.33	9.323%	$64.8613	$64.86	$64.85	$64.90
Purchase #4	$52.51	5.696%	$55.501	$55.50	$55.50	$55.50
Purchase #5	$179.67	11.113%	$199.6367	$199.64	$199.65	$199.60
Purchase #6	$151.56	10.821%	$167.9603	$167.96	$167.95	$168.00
Purchase #7	$144.74	10.507%	$159.9478	$159.95	$159.95	$159.90
7 purchase totals =	$857.63		$949.0784	$949.08	$949.10	$949.10