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	$19.76	5.668%	$20.88	$20.88	$20.90	$20.90
Purchase #2	$247.90	8.769%	$269.6384	$269.64	$269.65	$269.60
Purchase #3	$213.59	5.125%	$224.5365	$224.54	$224.55	$224.50
Purchase #4	$89.33	10.677%	$98.8678	$98.87	$98.85	$98.90
Purchase #5	$207.75	12.678%	$234.0885	$234.09	$234.10	$234.10
Purchase #6	$97.33	5.859%	$103.0326	$103.03	$103.05	$103.00
Purchase #7	$59.35	3.801%	$61.6059	$61.61	$61.60	$61.60
7 purchase totals =	$935.01		$1,012.6497	$1,012.66	$1,012.70	$1,012.60