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	$120.81	6.545%	$128.717	$128.72	$128.70	$128.70
Purchase #2	$50.58	6.787%	$54.0129	$54.01	$54.00	$54.00
Purchase #3	$6.92	13.315%	$7.8414	$7.84	$7.85	$7.80
Purchase #4	$157.88	6.730%	$168.5053	$168.51	$168.50	$168.50
Purchase #5	$49.86	8.590%	$54.143	$54.14	$54.15	$54.10
Purchase #6	$82.96	3.564%	$85.9167	$85.92	$85.90	$85.90
Purchase #7	$102.74	10.271%	$113.2924	$113.29	$113.30	$113.30
7 purchase totals =	$571.75		$612.4287	$612.43	$612.40	$612.30