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	$34.53	10.723%	$38.2327	$38.23	$38.25	$38.20
Purchase #2	$164.91	9.343%	$180.3175	$180.32	$180.30	$180.30
Purchase #3	$89.54	10.102%	$98.5853	$98.59	$98.60	$98.60
Purchase #4	$22.91	13.515%	$26.0063	$26.01	$26.00	$26.00
Purchase #5	$123.65	9.366%	$135.2311	$135.23	$135.25	$135.20
Purchase #6	$31.45	12.865%	$35.496	$35.50	$35.50	$35.50
Purchase #7	$17.86	3.472%	$18.4801	$18.48	$18.50	$18.50
7 purchase totals =	$484.85		$532.3490	$532.36	$532.40	$532.30