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	$42.48	4.676%	$44.4664	$44.47	$44.45	$44.50
Purchase #2	$39.27	6.769%	$41.9282	$41.93	$41.95	$41.90
Purchase #3	$232.63	3.389%	$240.5138	$240.51	$240.50	$240.50
Purchase #4	$40.92	7.337%	$43.9223	$43.92	$43.90	$43.90
Purchase #5	$106.47	12.647%	$119.9353	$119.94	$119.95	$119.90
Purchase #6	$83.57	12.542%	$94.0513	$94.05	$94.05	$94.10
Purchase #7	$67.58	6.757%	$72.1464	$72.15	$72.15	$72.10
7 purchase totals =	$612.92		$656.9637	$656.97	$656.95	$656.90