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	$19.55	13.216%	$22.1337	$22.13	$22.15	$22.10
Purchase #2	$242.43	11.734%	$270.8767	$270.88	$270.90	$270.90
Purchase #3	$148.44	8.674%	$161.3157	$161.32	$161.30	$161.30
Purchase #4	$148.28	7.576%	$159.5137	$159.51	$159.50	$159.50
Purchase #5	$56.88	4.709%	$59.5585	$59.56	$59.55	$59.60
Purchase #6	$59.98	3.304%	$61.9617	$61.96	$61.95	$62.00
Purchase #7	$97.28	3.206%	$100.3988	$100.40	$100.40	$100.40
7 purchase totals =	$772.84		$835.7588	$835.76	$835.75	$835.80