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	$46.59	9.538%	$51.0338	$51.03	$51.05	$51.00
Purchase #2	$19.50	7.576%	$20.9773	$20.98	$21.00	$21.00
Purchase #3	$8.60	5.215%	$9.0485	$9.05	$9.05	$9.00
Purchase #4	$53.76	11.413%	$59.8956	$59.90	$59.90	$59.90
Purchase #5	$176.76	12.285%	$198.475	$198.48	$198.50	$198.50
Purchase #6	$216.56	11.520%	$241.5077	$241.51	$241.50	$241.50
Purchase #7	$59.51	3.606%	$61.6559	$61.66	$61.65	$61.70
7 purchase totals =	$581.28		$642.5938	$642.61	$642.65	$642.60