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	$160.35	10.713%	$177.5283	$177.53	$177.55	$177.50
Purchase #2	$54.41	9.270%	$59.4538	$59.45	$59.45	$59.50
Purchase #3	$125.41	13.758%	$142.6639	$142.66	$142.65	$142.70
Purchase #4	$33.62	6.611%	$35.8426	$35.84	$35.85	$35.80
Purchase #5	$180.71	4.763%	$189.3172	$189.32	$189.30	$189.30
Purchase #6	$120.93	9.234%	$132.0967	$132.10	$132.10	$132.10
Purchase #7	$54.36	10.200%	$59.9047	$59.90	$59.90	$59.90
7 purchase totals =	$729.79		$796.8072	$796.80	$796.80	$796.80