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	$249.71	7.727%	$269.0051	$269.01	$269.00	$269.00
Purchase #2	$234.57	5.835%	$248.2572	$248.26	$248.25	$248.30
Purchase #3	$83.33	10.611%	$92.1721	$92.17	$92.15	$92.20
Purchase #4	$88.80	4.139%	$92.4754	$92.48	$92.50	$92.50
Purchase #5	$31.86	12.633%	$35.8849	$35.88	$35.90	$35.90
Purchase #6	$99.74	4.756%	$104.4836	$104.48	$104.50	$104.50
Purchase #7	$56.57	8.740%	$61.5142	$61.51	$61.50	$61.50
7 purchase totals =	$844.58		$903.7925	$903.79	$903.80	$903.90