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	$100.76	6.696%	$107.5069	$107.51	$107.50	$107.50
Purchase #2	$98.46	10.307%	$108.6083	$108.61	$108.60	$108.60
Purchase #3	$187.50	11.498%	$209.0588	$209.06	$209.05	$209.10
Purchase #4	$28.96	7.730%	$31.1986	$31.20	$31.20	$31.20
Purchase #5	$65.47	10.524%	$72.3601	$72.36	$72.35	$72.40
Purchase #6	$100.57	7.687%	$108.3008	$108.30	$108.30	$108.30
Purchase #7	$234.76	8.109%	$253.7967	$253.80	$253.80	$253.80
7 purchase totals =	$816.48		$890.8302	$890.84	$890.80	$890.90