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	$238.93	13.415%	$270.9825	$270.98	$271.00	$271.00
Purchase #2	$67.67	3.322%	$69.918	$69.92	$69.90	$69.90
Purchase #3	$228.78	8.102%	$247.3158	$247.32	$247.30	$247.30
Purchase #4	$171.42	13.215%	$194.0732	$194.07	$194.05	$194.10
Purchase #5	$78.59	13.297%	$89.0401	$89.04	$89.05	$89.00
Purchase #6	$21.86	7.514%	$23.5026	$23.50	$23.50	$23.50
Purchase #7	$81.80	8.807%	$89.0041	$89.00	$89.00	$89.00
7 purchase totals =	$889.05		$983.8363	$983.83	$983.80	$983.80