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	$240.33	12.713%	$270.8832	$270.88	$270.90	$270.90
Purchase #2	$97.60	12.457%	$109.758	$109.76	$109.75	$109.80
Purchase #3	$31.49	13.114%	$35.6196	$35.62	$35.60	$35.60
Purchase #4	$222.92	4.338%	$232.5903	$232.59	$232.60	$232.60
Purchase #5	$91.83	9.445%	$100.5033	$100.50	$100.50	$100.50
Purchase #6	$200.86	3.730%	$208.3521	$208.35	$208.35	$208.40
Purchase #7	$76.95	10.774%	$85.2406	$85.24	$85.25	$85.20
7 purchase totals =	$961.98		$1,042.9471	$1,042.94	$1,042.95	$1,043.00