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	$104.67	8.331%	$113.3901	$113.39	$113.40	$113.40
Purchase #2	$89.50	6.274%	$95.1152	$95.12	$95.10	$95.10
Purchase #3	$200.38	6.520%	$213.4448	$213.44	$213.45	$213.40
Purchase #4	$136.60	12.659%	$153.8922	$153.89	$153.90	$153.90
Purchase #5	$95.58	4.459%	$99.8419	$99.84	$99.85	$99.80
Purchase #6	$250.28	4.621%	$261.8454	$261.85	$261.85	$261.80
Purchase #7	$35.59	7.253%	$38.1713	$38.17	$38.15	$38.20
7 purchase totals =	$912.60		$975.7009	$975.70	$975.70	$975.60