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	$142.32	4.623%	$148.8995	$148.90	$148.90	$148.90
Purchase #2	$80.50	11.641%	$89.871	$89.87	$89.85	$89.90
Purchase #3	$191.48	3.736%	$198.6337	$198.63	$198.65	$198.60
Purchase #4	$75.84	10.611%	$83.8874	$83.89	$83.90	$83.90
Purchase #5	$61.44	12.669%	$69.2238	$69.22	$69.20	$69.20
Purchase #6	$166.27	11.553%	$185.4792	$185.48	$185.50	$185.50
Purchase #7	$100.47	6.544%	$107.0448	$107.04	$107.05	$107.00
7 purchase totals =	$818.32		$883.0394	$883.03	$883.05	$883.00