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	$89.40	11.478%	$99.6613	$99.66	$99.65	$99.70
Purchase #2	$71.43	9.280%	$78.0587	$78.06	$78.05	$78.10
Purchase #3	$206.88	12.413%	$232.56	$232.56	$232.55	$232.60
Purchase #4	$123.98	5.413%	$130.691	$130.69	$130.70	$130.70
Purchase #5	$43.74	13.427%	$49.613	$49.61	$49.60	$49.60
Purchase #6	$176.78	12.758%	$199.3336	$199.33	$199.35	$199.30
Purchase #7	$198.35	5.665%	$209.5865	$209.59	$209.60	$209.60
7 purchase totals =	$910.56		$999.5041	$999.50	$999.50	$999.60