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	$150.31	9.412%	$164.4572	$164.46	$164.45	$164.50
Purchase #2	$12.38	3.384%	$12.7989	$12.80	$12.80	$12.80
Purchase #3	$206.48	8.302%	$223.622	$223.62	$223.60	$223.60
Purchase #4	$120.49	5.709%	$127.3688	$127.37	$127.35	$127.40
Purchase #5	$174.74	9.765%	$191.8034	$191.80	$191.80	$191.80
Purchase #6	$223.30	4.795%	$234.0072	$234.01	$234.00	$234.00
Purchase #7	$35.33	7.362%	$37.931	$37.93	$37.95	$37.90
7 purchase totals =	$923.03		$991.9885	$991.99	$991.95	$992.00